Thanks for all the help guys!
Unfortunately my video card is too old for soft 15hz.
I'm using the configuration utility with advancemame right now.
I'm stuck again though... I can't find anything about the pixel, horizontal or vertical clock speed in the service manual for my monitor.
I guess...
I'm hooking up the J-PAC adapter tonight in my Neo Geo cab. Its a conversion from an older Defender cab. The monitor itself (the glass) has an RCA sticker on it, but the board has a model number: Wells Gardner 19K4901.
The manual on the Wells Gardner model number says it runs at 50 hz - 60 hz...