In the spring of '21 I bought an iPhone 12 Pro Max with 256 gigs. But after three years the phone had been running out of space, and so I recently decided to trade it in for an iPhone 15 Pro Max with 512 gigs. The idea was that I would back up the contents (photos, apps, music) to the cloud, but I hadn't backed it up since last November, and it took hours and hours to manage this. And then when I tried to load the contents of the 12 onto the 15, it had only captured about 60% or 65%. So I went to the local Apple store and asked them to do a phone-to-phone transfer, which would deliver an exact duplicate of the 12. I showed up when the store opened at 11 am, and it took all day and still didn't complete the task. I had to leave it there overnight. I returned the next morning and the phone-to-phone had finally completed. All in all the whole process took several days.