Assuming you are using an arcade monitor (you didn't say?)
Maybe take a look at the Trident Blade T64.
You can also try your luck with Powerstrip and a compatible video card, I'm using it with a TNT2 with so-so results.
But realize that none of these will boot at 15KHz, so you have to take precautions to not damage your monitor while you wait for the system to start outputting a 15kHz signal.