Most of the Jensen and ASI radios do use a 10 amp fuse. Depending on what else Keystone wired into that circuit (maybe the WINEGARD TV Amp, etc) a 15 amp fuse could be needed for that leg of the wiring. If the fuse panel calls for a 15 amp fuse, I'd be reluctant to install a 20 amp on a permanent basis. You might be OK and than, you might wind up with some melted insulation and burned wiring after it sits for a couple of days. Then again, it might "torch" the wiring in an hour or two. That's reason enough, to me, not to exceed the fuse rating that's marked on the circuit.
If your radio is a Jensen, you can give their technical support section a call at 877-305-0445 M-F 8AM to 6PM Eastern Time. Or you can email them from this link:
http://www.jensenrvdirect.com/technical-support
If you're still in warranty, this is one for the dealership. If you're out of warranty and have considered upgrading to a better radio, this might be an excellent time to start looking for what you prefer as a replacement.