I had two iPhone 15 Pro. I'm sure the second Pro had it. It is easier to spot if you compare the display with a display of an iPhone with LCD display. I could it see better on darker colours like red and with low adjusted brightness. Personally I think it is the Mura Effect as described
there and I think many iPhones are affected but people don't notice it because they operate with higher brightness adjustments. But I never experienced the screens as "dull".
The first iPhone 15 Pro had a really aggressive angular color shift, the second less but still disappointing, so that is a problem too. The first was built November 2023, the second October 2023, the second had a LG display.
I returned my iPhone 15 pro twice. The first one also had a really aggressive angular color shift, going from teal to pink, with some sectors of the screen being teal and others pink looking at it straight-on, so I exchanged it.
The second unit fixed that issue, its color shift was slightly less pronounced and went from blue to yellow-orange (much more comfortable on the eyes,) but it had an even worse issue: the Mura effect you described. It was so intense I thought it must've been a graphics driver issue or something like that, but it didn't go away after a software update. I returned it again.
The current third unit has a bit of both. It has the same teal-to-pink shift, but less intense partially due to the gradient being slanted for whatever reason. The Mura effect is still present but to a lesser degree and has a faint horizontal line pattern. When looking at a white background, the texture looks similar to the texture of Minecraft wool elongated on the x axis.
I think all units had an LG display. I got them all from the same Apple store. If anything, the first one could've been a Samsung display as I didn't notice the Mura effect/grain (maybe because I was so distracted by the intense color shift + I didn't have it for long,) but I doubt it was Samsung as I think their QC would have had higher standards to not allow such intense color shift.
It really sucks to see Apple start having quality control issues this bad. They must realize the vast majority of their consumers are people who aren't of the enthusiast-kind that notice when something isn't quite right with their device; they're folks that just wanna have an iPhone! So cutting down on QC to save money must be reasonable to them. I wish it wasn't considered overly meticulous for someone like me to demand a display that doesn't have any of these problems, at least in the eyes of Apple. It's a thousand dollar phone after all that I plan to have for many years and I think everyone here would agree with me that no one should have to deal with this in the first place.