I use a 16 gauge, 100ft cord on mine with a 30 to 15 amp adapter at the MH. I then plug the cord into an outlet in my barn.
I check the extension cord connectors for heat or discoloration, fell the connectors, if they are warm, the connectors are probably dirty and starting to go bad.
If you are just running it to keep the battery charged and/or the frig cold, 16 will be OK.
16 guage cord OR your 15 amp circuit will not be big enough to run the A/C or a portable electric heater.
2001 Coachmen Mirada (Ford F53 6.8L V10) - Toad 2003 Saturn Vue.
It won't do MACH 2, but I can get a sandwich and take a pee.