because my iPhone would not put calls through at all (and no, I had none of the "Focus" features or call forwarding or other muting features enabled). Ultimately they had to update the network settings on their end, but it took me going through more than 8 people to get someone to do that.

Security alone motivated me to update and it isn't clear to me this occurred as a result of the IOS 15.1 update nor was an Apple issue, but just be aware...

Backup regularly.

both my iPad and iPhone downloaded and kept hounding me to install to the point I became intensely irritated. I read up on "whether to update or wait," decided there might be some security benefits, backed up, and went for it when I had the day off. Honestly, both devices did so without any problems (I even got some songs and some of the artwork for my music that had disappeared back).

But yeah. I'd liked to have stuck with 14 for a while longer.