I need one that can do 15Hz, is that right?
Yes. There are a few out there that can do both 15Hz + 31Hz. The one I use for that is the NEC Multisync 1970NX (19"). I'm not a huge fan of being off the natural resolution of an LCD as it causes some soft blurring. But the NEC monitor does a very nice job regardless.
As a general rule for big boxes the cable is buffered. For the all-in-ones, unbuffered. There's a guy on Amibay who goes by "a.mi.goun" that makes and sells brand new hand-made cables
. Very high quality should you ever need one. I got one of each about 2 years ago.