Other than Beaches, I can't see why all of the restaurants couldn't accommodate a party of 15. You'd have to spilt up into cars at Sci-Fi but you'd all fit. We did 15 at Marrakesh and it wasn't an issue and the belly dancers were cool. I'm guessing the biggest issue will be getting the seating time you want.
For fun maybe HDDR? Or Coral Reef? That big fish tank is pretty cool for the kids.