You know how usually you can't restore from iCloud between major versions. Looks like they're now doing that with minor versions also.
For context, I 'shift+restored' back to 15.1 and then when phone came on and I logged into iCloud, I selected the latest backup and it then said 'in order to restore from this backup you must remain on the developer beta program' so it then updated me back to 15.2 and restored from iCloud.
Hopefully there is a workaround as i'm sure someone will need to take their phone in for service at some point and won't be able to without being on a 'release' version.
There is a work around but I haven’t had to use in ages. So I’m a little vague, but got enough info for you to research more.
You change the log file in the archived back up in finder/iTunes from 15.2 to 15.1, then your back up is excepted on the older iOS when you restore.
If you don’t need to restore though, just flash 15.1 on, finder/iTunes alt/shift click on check for update button, select the IPSW you’ve downloaded. Reinstalls the iOS like an update, doesn’t touch data or apps. Is worth a shot.