Leaking valve connection, recent shower install
I would definitely look at cutting an access into the drywall instead of removing tile. You'd have to remove a lot of tile to get in there and redo that connection. Dry wall is easy to fix. You should frame it in afterwards for access in the future. Just make absolutely sure you know where the water is leaking from. It could be another location and pooling at the point you see it. If the installer has a guarantee, I'd be getting him back there. good luck and stay safe out there.