I tested the iPhone 18 Pro Max vs. iPhone 15 Pro Max side-by-side: Is it time to upgrade?

In my last face-off, I drilled down into all the differences between the iPhone 18 Pro Max and iPhone 16 Pro Max. There wasn’t a huge difference across the two-year gap separating them — but now I’m going further by taking the iPhone 15 Pro Max for a spin.

As I’ve said numerous times before, three years is the bare minimum you should wait before thinking about upgrading to a new phone. That’s exactly what I’m tackling in this iPhone 18 Pro Max vs. iPhone 15 Pro Max face-off, where the differences on paper are much more substantial.

But looking at specs doesn't give a clear-cut indication of how much of a difference three years actually makes. That's why I’m going to show you whether there’s enough of a generational leap to justify making the switch.

iPhone 18 Pro Max vs. iPhone 15 Pro Max: Specifications

iPhone 18 Pro Max vs. iPhone 15 Pro Max: Cameras

Just as before, camera performance is tops on my list because it’s the feature I rely on most. The iPhone 18 Pro Max clearly benefits from having the latest hardware — a 48MP triple-camera system complete with a mechanical variable aperture on the main lens. Other notable advantages for the iPhone 18 Pro Max include a wider maximum f/1.48 aperture that inherently allows more light to hit the sensor, as well as the wider field of view from its 18MP Center Stage front camera.

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Beyond the hardware, the appeal of the iPhone 18 Pro Max lies in its Pro Controls for granular exposure adjustments, along with significantly improved video modes. For example, it can record 4K footage at 120fps and includes pro-video features I crave, such as Log recording, Cinematic mode, smart focus tracking, ProRes support, and Audio Mix.

From both a hardware and feature standpoint, the iPhone 18 Pro Max makes a compelling argument — enough to make an upgrade seem like an open-and-shut case. But hold that thought until you see the side-by-side snapshots below.

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Honestly, I was hoping for a much wider divide between their camera performances, but the iPhone 15 Pro Max holds its ground in most situations. Under ideal conditions, the 15 Pro Max’s main and ultrawide cameras produce nearly the same results as the iPhone 18 Pro Max. You can see this in the daytime shots around Bryant Park, the macro flower close-up, the panorama, and even in how both phones neutralize harsh highlights.

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Interestingly enough, the iPhone 15 Pro Max’s 12MP telephoto camera with 5x optical zoom actually delivers sharper results on the apartment building graffiti shown above. While the iPhone 18 Pro Max holds a clear advantage at 4x, the 15 Pro Max pulls out finer detail at 8x and 40x zoom by leaning on its dedicated telephoto shooter.

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Where I do see a substantial leap is with the iPhone 18 Pro Max’s 18MP Center Stage camera. It captures noticeably crisper definition and provides a wider field of view, making it far better suited for group selfies.

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Lastly, the iPhone 18 Pro Max has the edge in low-light performance — but primarily in near-pitch-black settings. In the gallery shots along the beach boardwalk, there’s very little difference between them because ambient glow from the street lamps illuminates the scene.

But in my backyard where there’s virtually no ambient light, the iPhone 18 Pro Max clearly boosts shadows to draw out details that are otherwise lost on the 15 Pro Max.

iPhone 18 Pro Max vs. iPhone 15 Pro Max: Battery and charging

Because it’s a physically bigger device, Apple packs a much larger 5,391 mAh battery inside the iPhone 18 Pro Max — compared to 4,422 mAh in the 15 Pro Max. That translates to roughly a 22% increase in battery capacity, but our test results show that Apple has also made massive strides in power efficiency.

In our custom battery drain test, the iPhone 18 Pro Max clocked in at 18 hours and 27 minutes, which blows past the 15 Pro Max’s 14 hours and 2 minutes. That’s a 4-hour and 25-minute difference — a 31.5% improvement in endurance — that I credit largely to the efficiency of the A20 Pro chip. In day-to-day use, the difference is night and day.

Charging is also significantly faster across the board, both wired and wireless. In just 15 minutes over USB-C, the iPhone 18 Pro Max reaches a 53% charge, compared to just 20% on the 15 Pro Max.

iPhone 18 Pro Max vs. iPhone 15 Pro Max: Performance

Both phones feel fast and fluid during everyday tasks, thanks to their 120Hz ProMotion displays. But for more processor-intensive workloads — like editing 4K footage or playing demanding games — the newer A20 Pro chip holds a decisive advantage over the older A17 Pro. Simply put, there is no contest.

Looking at our Geekbench 6 scores, there's nearly a 2,000-point spread in single-core performance and a massive 5,800-point gap in multi-core. That translates to a 70.4% leap in single-core speeds for the iPhone 18 Pro Max and an even larger 84.2% boost in multi-core muscle.

While those CPU gains are substantial, the iPhone 18 Pro Max’s graphics performance is where the generational gap truly widens. In 3DMark’s Solar Bay Unlimited test, the iPhone 18 Pro Max averaged 67.9 fps, making the 15 Pro Max’s 23.9 fps look choppy by comparison. That represents an astonishing 184.1% leap in graphics capability — a gain bolstered by the 18 Pro Max's redesigned internal vapor chamber, a cooling advantage the iPhone 15 Pro Max lacks entirely.

iPhone 18 Pro Max vs. iPhone 15 Pro Max: Software and AI

I won’t spend too much time hashing out their software and AI features because they’re practically identical — save for a couple of details. That’s the beauty of Apple supporting older flagships with its latest platform update: iOS 27. The release brings the older iPhone 15 Pro Max to near-complete parity with the iPhone 18 Pro Max, delivering the Liquid Glass interface, refreshed customization tools, and core system tweaks.

The most visible functional difference comes down to the Dynamic Island and how many Live Activities it can handle simultaneously. Thanks to the redesigned, slimmer cutout on the iPhone 18 Pro Max, it accommodates up to three Live Activities — compared to just two on the 15 Pro Max.

Under the hood, the iPhone 18 Pro Max packs 12GB of RAM, granting it extra processing muscle for the most demanding, on-device Siri AI workflows. In day-to-day practice, however, these distinctions hardly tip the scales, as the iPhone 15 Pro Max retains full access to the broader Apple Intelligence suite.

iPhone 18 Pro Max vs. iPhone 15 Pro Max: Displays

Beyond the bump from a 6.7-inch panel to a larger 6.9-inch Super Retina XDR display with the iPhone 18 Pro Max, the biggest upgrade here comes down to raw outdoor visibility. In our display testing, the iPhone 18 Pro Max hit a peak brightness of 2,326 nits — compared to the 1,550 nits measured on the iPhone 15 Pro Max.

That works out to a massive 50.06% increase in peak brightness, which is instantly noticeable when I’m outside with the sun glaring down on their screens. While the 15 Pro Max is still visible, the extra brightness just makes the 18 Pro Max much easier on the eyes.

iPhone 18 Pro Max vs. iPhone 15 Pro Max: Verdict

The evidence points to an obvious conclusion: the iPhone 18 Pro Max delivers a substantial enough upgrade to convince at least some iPhone 15 Pro Max owners to make the leap — even with Apple asking $100 more for its flagship.

From the raw muscle of the A20 Pro chip and a battery that lasts more than four hours longer, to its upgraded camera hardware and professional shooting tools, this comparison proves that three years remains the sweet spot for upgrading. However, if your iPhone 15 Pro Max still offers good battery health, you can probably get by at least until Apple unveils the iPhone 20 next year.

While day-to-day photo quality remains neck and neck in most scenarios, the iPhone 18 Pro Max pulls away in other areas. Between the mechanical variable aperture on the main lens, dedicated Pro Controls, and an expanded suite of pro-grade video tools, it offers more than enough tangible upgrades to justify the jump for power users.

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