Check with IT & Co-Workers
If you use your iPhone or iPad for work, you'll want to check in with IT (if you have a department) and your co-workers before you make the move.
Enterprise problems are extremely common after iOS updates and we typically see complaints about apps and other services emerge in the hours, days and weeks after release.
So, it would be smart to check in with a professional if you can. If you're lucky they were using the iOS 9.2.1 beta ahead of the release.
If you don't have an IT department, check in with your co-workers to see if key apps and services are working after the iOS 9.2.1 update.