The AC will use 5 amps more during hard starts, converter about 6 amps so yes you can use a 20A (assuming it is there and works). However it is surprising how much your "needs" for current can grow the coffee maker, the electric fry pan...
a number of us have a Progressive Dynamics 4045
http://www.progressivedyn.com/all_in_one_pd4000.html which simplifies the electrical