Do you have a portable appliance you can plug into the 15 amp utility outlet to see if there's power there? That would be a start any way. Do you have an onboard generator? Have you tried running it to see what happens? A failed automatic transfer switch could be causing your problem.I'm plugged into 30A now, I had a 15/30 converter on before. Same result though
If the rig has a transfer switch, that might be where the power is being lost.