Hello.
If I install a 3 horsepower 120VAC single phase motor and the compressor it has to drive uses/needs only 2 horsepower 120VAC single phase; leaving aside -ignoring- starting current; would the 3 HP motor consume only 15 Amperes from a plain outlet/breaker when running ?

 

would the 3 HP motor consume only 15 Amperes from a plain outlet/breaker when running ?

For a typical single-phase small AC motor with a efficiency of about 80%, the power draw would be about 746/0.8 = 933W per HP, so for 2 HP, the draw would be (933*2) / 120 = 15.5A,