A generator needs to be 3 to 4 times more wattage than the compressor load so with a 15amp electric motor at start (LRA) will draw 6 to 10 times it's FLA listed on the motor. So a generator that can steadily put out 50 to 60 amps is required to start the 15 FLA motor under load. If you get a replacement motor make sure its the same volts, FLA (full load amps) and RPM. A lower RPM motor can be used but the drive pulley and belt has to be changed.
a 240 volt only "SPL HP" motor usually is sold as a "5 to 6HP" marketed compressor by Loews, Sears or Sanborn, they usually draw 15 amps at 240 volts and produce an actual 3HP output. At 9.5 to 10 amps measured under load that translates to about 1.5 HP actual motor output. your motor sounds a bit weak for a compressor unless it was originally a 1.5 HP dual voltage model 120/240 volts. Running a compressor at 120 volt at 20 amps is not very useful, pops breakers, overheats plugs, melts outlets, etc. Your model and make of compressor will narrow down your selection of replacement motors and the cost as well.
My kid asks me questions all of the time, I never say "that's a dumb question". Gave her my old cell phone and when stumped with some question I just say "honey, I don't know everything in the world, Google search on your phone" I try to reward her curiosity not discourage it!
I told my boys to either pay attention to what I'm doing and learn how to fix things...or make a lot of money so you can pay someone else to do your man work. So far, they haven't done either one and didn't listen to a thing I said. Back to the issue...about 9.5 -10A on each side with inductive. Comes to maybe 3 or so if I am close. Matches up. I found a motor that looks like it should work perfect. I'll give that as try! I think I screwed the motor up years ago when I did some very improper wiring just to get it up temporarily...involving a couple regular extension cords running to a couple different 15A circuits and maybe a generator. I just remembered that. I remember it smoking some at the time periodically.