I really wasn't ready to believe that this would do anything but since I also had an old sim card laying around, when I came across your post I thought there's probably no harm to give it a go at least. I didn't toggle the cell data on though, just shoved an old sim card in and hit install. I have a iPad Pro 9.7" and now it's updated from 15.0 to 15.0.2 without issues.Here’s how I finally updated my iPad Pro 2nd gen to 15.0.1 last week and to 15.0.2 today…was having same issues as everyone else here; stuck on “verifying update” part no matter what I tried to make it update. I have a cellular model but no active plan on it currently…had an old SIM card laying around and figured what the heck, let me put it in and see what happens…I toggled the cell data button on and went to download the 15.0.1 again, and guess what, actually updated this time!!! (turning on cell data, even with a non working sim, somehow triggered something to update the OS 🤷🏾♂️
There’s one thing I should clarify: you have to delete the previously failed download by going to settings>general>iPhone storage and manually delete the 15.0.1 file as rebooting will not automatically delete it
Hope this works for y’all, as it did for me!
Hopefully this won't become a habit, but I'm definitely keeping this whole sim card thing as a regular troubleshooting tool to these issues from now on.