tl;dr This is a comparison post between the iPhone 15 Pro and an iPhone 13 Pro.
The story:
I'm a semi-professional photographer and videographer, I have a Nikon DSLR and a bunch of professional (fast) lenses, a professional cinematography drone, and I experiment with professional photography, videography, and audio.
My wife had her iPhone 13 Pro and I had a Google Pixel 8 Pro. Every week or two, wireless Android Auto on my Pixel 8 Pro would stop pairing and projecting to my car's screen (a '23 Acura Integra) and fall back to Bluetooth-audio only.
Needless to say, this was pretty infuriating. As okay as I am with audio-only, having GPS maps projected to the car's screen vastly improves quality of life and safety when driving (especially to new clients) as I primarily rely on visual observation for directions.
Eventually, I got completely fed up, and after a particularly horrible Thanksgiving dinner with my in-laws where my brother in-law decided to not only come out of the closet but also announce his transition using a ventriloquism dummy (it was very... interesting), I chucked my phone out the window on the highway while we were driving home. (The scotch I drank may have contributed to this)
Anyway, family drama aside, I bought my wife an iPhone 15 Pro for Christmas and she gave me her iPhone 13 Pro. I got a battery replacement recently and I'm happy to say that Apple CarPlay has worked near-seamlessly for as long as I've had it.
The iPhone 13 is truly the best (most bang per buck) phone for average daily use.
However, seeing as I have access to my wife's iPhone 15 Pro, I've also had the opportunity to use that, and this is what I have to say:
If you do any kind of professional photography or videography with your phone, or if you are simply looking for professional-level quality in your photos and videos, then get an iPhone 15 Pro. The extra $300 for the upgraded 48 MP primary camera and 60 FPS 4k HDR video capabilities is worth it, especially considering what you'd be shelling out for a separate device with those capabilities.
The iPhone 13 Pro has slightly faster lenses with the main camera and ultra-wide camera (f/1.5 and f/1.8 on the 13 Pro vs f/1.78 and f/2.2 on the 15 Pro for the main and ultra-wide respectively) but the sensors have less megapixels. Overall, this doesn't matter as much even for professional photography except in niche cases.
Let's be honest: if you truly needed an ultra-fast lens at a professional level, you would probably get an f/1.4 on a mirrorless. f/1.78 for the main camera lens with 48 Megapixels (iPhone 15 Pro) is easily on par with a Nikon 850 DSLR paired with an f/2.2 70-200mm telephoto, a setup that would cost you about $2k.
Point being, the iPhone 15 Pro cameras are much better than the iPhone 13 Pro just on account of detail and megapixels, despite the (slightly) slower lenses. You'd be paying considerably more for a dedicated professional camera to have that level of performance.
(And yes, I understand full-frame and cropped sensors and I understand that a professional full-frame camera produces more detail than a phone ever will, but the phone is far more convenient, and it's quite something to be able to say you can take nearly the equivalent photo of $2k worth of professional equipment with your cellphone)
USB-C on the iPhone 15 Pro is super nice for transferring large files (e.g. 4k media), but it doesn't matter for charging because we only use wireless charging, either Qi or Magsafe, to prolong the lifespan of our ports. (I've often found charge ports to be the least physically resilient aspect of the phone and retired more than one phone due to a faulty port)
USB-C on the iPhone 15 Pro only makes a difference for high-speed data transfer of (many) large files (e.g. 4k HDR video and many hi-res photos). Wireless data transfer from iPhone to Macbook is far more convenient and my preferred choice.
I only revert to USB-C when I have a lot of data to transfer from the iPhone 15 Pro.
Having that handy action button on the 15 Pro tied to the camera is incredibly useful, but you can absolutely live without it and not even miss it. I see the action button as minor because I can definitely live without it without caring.
For reference, https://www.macrumors.com/guide/iphone-13-pro-vs-iphone-15-pro/.
Past that? Dynamic Island on the 15 Pro doesn't matter. Titanium material and reduced weight on the 15 Pro doesn't matter (stainless steel is great!) Chassis color choices on the 15 Pro aren't nearly as good as on the 13 Pro. Always-on screen has always been useless for me, that's the first thing I turn off – but I practice remaining disconnected from my phone because I consider it a "necessary evil."
Action button is nice, but I don't find that much added utility, even for quick-draw camera. Having a camera shortcut icon on the bottom strip is nearly as fast and not particularly inconvenient thanks to Face ID and fast unlock. Action button itself hardly makes enough of a difference to matter (I wouldn't pay extra for it) but now that it's here, I appreciate it and hope it stays.
Everything else on the iPhone 15 Pro is incremental and largely unnoticeable at best compared to the 13 Pro.
For professional photos and videos? Get an iPhone 15 Pro. For everything else – there's iPhone 13 Pro.