Depends on how u wire the amp.....at 1 ohm with the gains down, the sx would do well, or at 2 ohms with the gains up....for the se, at 2 ohms with the gains down quite a bit........
I have that exact set-up with one 12 SE running off the BX1000d in a 2.25 26hz tuned box and the sub is getting all that it wants. The only reason I'd consider getting the BX1500d is if you were planning on getting another SE in the future so you could run 2 SE's @ 1ohm with your 1500d.
isnt the bx1500d somewhat over-rated?? so at 2 ohms an SE would get less than 1000 watts. Also i've heard people recommend giving SE's 800 watts. would it all come out to be about right wattage wise?