No, that voltage is way high, you have a problem somewhere. On a GM chassis the voltage regulator is internal to the alternator, so it gets replaced not repaired.
Usually there is a circuit breaker in the charging circuit to the house batteries to prevent high current but not high voltage. usually if there is a problem with the battery you will see high current not high voltage.
I would measure voltage at the coach battery with the engine running and see if you get the same 15.4v, if so them my money's on a bad alternator. If you get a more normal 13.6 at the coach battery, then the alternator is OK and the problem is somewhere on the house side, potentially a bad battery.
Are there other charging sources like solar connected to the house battery? If so that charge controller may be causing the problem by not dialing back the power when the alternator comes online.
I would also house measure battery voltage when connected to shore power, it's possible the charging circuit in the converter is bad but that's unlikely.
