Originally Posted by
mikegss
My wife has the A15 (a very slightly higher spec phone), she's also had the update but has no problems. It's a mystery...
Possibly there's an app on your phone which doesn't work well with the system upgrade?
Pretty hard to diagnose but something which is running all the time, like a fitness tracker, would be a possibility. You could try stopping any likely candidates and see if that does any good.
First step is probably restart the phone in safe mode (assuming it gives you that option).