Newly leaked images and a video purportedly of a case for the forthcoming iPhone 15 Pro appear to show many very small alterations to the size and position of controls.
The cutout for the button is noticeably smaller than that for the old switch. That would fit the claim of Apple changing to a button since that would need to only be pressed, not slid to one side or the other as at present.
While that cutout is smaller than the current equivalent, the leaked images appear to show the the one for the bottom charging connector is larger. That also fits the expectation that Apple will switch from Lightning to USB-C for the iPhone 15 Pro.
It appears that the sleep/wake button, and the volume buttons, are the same size as before, but positioned fractionally lower down the side of the chassis.
The most significant difference revealed in this video is that it appears that the iPhone 15 Pro will feature a slightly larger microphone grill, and also that the camera section will be bigger as well.