Sure you can run a he-man amp off a 15 amp line, but it will never perform as it could at any volume level. Think transients and dynamics. Not to mention the amp will run cooler. Hell, I upgraded the line to my Poineer AVR from 15 to 20 amps and can clearly hear the improvement.
On a side note I have run Big NAD , Anthem , Bryston , Krell , Rotel , B&K amps off this very unit and never ran out of juice. Again remember that unless your running full power max volume and taxing the amp , you will never need any more juice.