I don't know if the RV charger is a quality Smart 3/4 Stage Charger or a quality more expensive Inverter/Charger (sort of doubt that if its the original equipment) or a cheaper Converter Charger or its amp capacity, so I cant speculate on how well or how fast it will charge your house battery.
That being said, if you turn off everything in the RV except for the Charger circuit and plug the RV into a standard 15 amp 120 volt house outlet even with 50 ft of cord and adapters it could (subject to Charger size and current draw) still sufficiently charge the RV house battery eventually. If its a cheaper Converter/Charger it will take longer,,,,,,,,,If its a Smart 3/4 Stage Charger it can charge it faster SO LONG AS ITS CURRENT DRAW DOESNT EXCEED YOUR 15 AMP SOURCE AND A LONG CORD CAPACITY.
TRICKLE CHARGER OR BATTERY MAINTAINER OPERATION
Those are usually very low amp units, maybe 1 or 2 amps and I see no problem using a 15 amp receptacle and 50 ft of cord to operate it. However if the RV battery is badly depleted it could take a longgggggggggg time to bring it to a full charge and even if so its NOT the quality and complete level of true full charge a Smart charger could achieve. Those are more for battery maintenance over winter or long storage periods then they are as real battery "chargers"
I would guess the RV's built in Converter Charger (even if original and NOT a Smart Charger) will do a much better job as its likely at least a 30 or more amp unit then a 1 or 2 amp trickle charger battery maintainer PROVIDED THE 15 AMP CIRCUIT AND CORDS HANDLE IT which I think will if all else in the RV is off.
John T Long retired electrical engineer so no warranty