do you have a particular budget? Any amp that will do the 1500 at 1ohm will do 1500 or more at .5 but it may not be recommended to run that amp at such a low impedance. contact manufacturer or check forums for running "blank" amp at .5 as for an amp at 2 ohms... once again your options are endless... view sites and specs and find something in your budget. but for .5 your gonna have temperature issues and possible damage.
There are plenty of amps that put out 1.5Kw @ 2 ohms.
Avoid trying to run at ultra-low loads like 0.5 ohms though, as this stresses any amp power supply and leaves very little reserve power for sudden demands in current and poutput. At least at 2 ohms, you'll have reserve power available in a good amplifier for those sudden bursts of output that a sub will require.
a used Orion 2100HCCA will do 800WRMS x 2 @ 0.5 ohms, or 1600WRMS x 1 @ 1 ohm bridged... but it's going to require a LOT of current to do that (class AB amp) and it runs extremely hot.
http://www.lightav.com/car/amps/poweramps.html i ran into this website a while back wen i was looking for an amp that can push 1000 watts at 2 ohm. its a list of all the best amps in order based on power output. there are amps that run at .5 ohms
