1 15 vs 2 15's

I hear the discussion of one 15 vs 2 12s all the time but I wanted to ask the question of 1 better 15 vs 2 lower 15's, for this is the crossroads I'm at. To be more specific I have a audiopipe apcl-1500.1d amplifier, that according to the dyno's I've seen, rates around @1 ohm certified 1400...