Problems after 15.1 upgrade
After the update my network (4G) keeps falling out. Wifi seems ok.
I have to turn my phone off and on again to get it working :-( Happens multiple times a day.
Question marked as
Check Settings, General, About and check for a carrier update.
With the phone powered on, take the SIM out and rub the contacts with clean cloth and put it back.
See also the various suggestions in the support article below but if they don't help, and your network carrier can't help, then contact Apple Support for further investigation.
Support article:
https://support.apple.com/en-us/HT201415