I just recently upgraded to the iPhone 15 (not the Pro) and had some frustration with the process. The first was the so-called "Quick Start" feature. My previous iPhone was a 12 and it would present the Quick Start Prompt, but the 15 would refused to connect and start the process. The 12 was running iOS 17.2.1 and did have Bluetooth enabled (which I believed is evidenced by the prompt to use Quick Start on the 12), but that was as far as it got. Ultimately, I had to use an iCloud back up to do the update and that worked as expected. So, in the end, I am setup. I will say that the transfer of service (using eSIM) was a perfect experience with AT&T. It was much better that the experience I had updating my Pixel 6 to Pixel 8 on T-Mobile. That was also frustrating (perhaps a blog entry for another time).
Another frustration was using Apple's Support Chat. Evidently, they have "improved" it by enabling some AI features. The Chat could not understand the problem I explained and kept referring to support articles on using iCloud and not helping me with Quick Start. I still don't know if I ever reached real support person, or was just dealing with unhelpful assistance from a 'bot.
One last little frustration was the changes to Face ID. Recently, Apple added "Face ID with a Mask" which seems like a great idea for the current endemic environment humanity is in. They also now added Glasses detection, but it seems to be tied to "Face ID with a Mask" and not generic Face ID. I am not sure how this different. I added it any way using three scans of my face with and without glasses. It does seem to work, but is a little tedious. I should pointed out that the Glasses detection does not work with Sunglasses (according to the support article) so keep that in mind when using the iPhone in the daytime outdoors.