New SEPM good, clients still old defs

We've decided to create a new server to use with SEPM 12.1.5. Everything is fine except no clients (12.1.4) are updating. I've tried to push the updates but nothing. The clients can see the server. The clients are still at 3/20/2015. Would that be an issue for SEPM to handle? Do I need to manually update with a newer def file for it to work?