I went from an 11 Pro to a 15 Pro and I share your feeling that it isn’t that big of an upgrade. The photos, especially in low light, aren’t that much better. In fact, I even think my 15 Pro camera has a blur problem. A lot of photos are blurry, less sharp than photos taken on my 11 Pro. There are others that report similar issues: https://www.reddit.com/r/iphone/comments/16z7fmb/brand_new_iphone_15_pro_blurry_camera/
Video does look better. But recording 30 fps portrait video still shows some stuttering some times.
A universal back gesture doesn’t make any sense. Windows Phone had a dedicated back button. Which was a mistake. There are many situations where there isn’t a logical “back”. It should only be available when it makes sense.