I run a 12 gauge 50' cord from my garage into the 30' rv cord with a hockey puck adaptor. It will run my 15k ac with no problem. This is from a 20 amp circuit.
I don't do this, but I can do it. I j normally use this setup to keep my battery charged year around and to run the two fridges in my trailer.
2012 Toyota Tundra 5.7 Litre DoubleCab
6 speed, 4.30 Limited Slip, Tow Package
2013 Jayco White Hawk 27DSRL
2010 Jayco JayFlight 26BH sold
Yamaha EF2000is Generators (2)
1996 Honda CB750 Nighthawk