Can I hook up to a house from a 30A plug to a 15A circuit

Small problem for a trained licensed experienced electrician. There are several solutions here and we have read some. When I had a 30A RV I wired a cord to an outlet inside my Dolphin to use a heater on the 15A 120 volt outlet found at most RV parks next to the 30A and 50A receptacles. When I boondocked in a driveway I had the 30A on one circuit in the host house and the heater cord to another outlet on a different circuit in the host house.