I believe the power rule of thumb is to add 15-20% for lost efficiency.
Therefore 800w = 960w and 600w = 720w.
Your maximum draw would be 1680w which if your American, would be just over 15 amps.
It might work, especially if your 600w rig isn't actually drawing 600w. Most 15 amp breakers only trigger after sustained 15 amp loads, which I don't believe you'll see.
Are you sure it's on a 15 amp breaker or are your referring to a single 15 amp wall plug?
Some people do but I wouldn't recommend max loading any circuit. Better off getting anot her circuit put in for your miners and make it a 20amp. Better safe than sorry