If you must plug into a 15 amp socket you might look into getting a kill-a-watt. Amazon.com: P3 International P4460 Kill A Watt EZ Electricity Usage Monitor: Home Improvement
Plug it into the desired socket then plug the RV into the Kill-A-Watt and it should tell you how much current your rv is drawing.
One should also take care in where you plug it in. Was the socket installed according to code by an electrician or by "Billy Joe Bob" from down the street. I plugged my RV into a socket in a storage shed and went about my business. A short time later everything quit so I went to check the circuit breaker only to find it had NOT tripped. After looking around I also noticed the light switch in the shed had melted. I replaced the switch and immediately had a 30 amp circuit installed. So just be careful.
Also when calculating amps that a device takes, don't forget to factor in startup surge. a device may run at say 5 amps but it may take considerably more to get it started albeit briefly.