I have a visa versa situation - my BenQ FP222W does 15 kHz on Windows against the spec which starts at 24 kHz. But running outside of the spec it may be picky - earlier I just got out of range messages but then something may have been changed on NVidia drivers so now custom screens from 320x200 up do work. But timing might be critical - haven't tested Amiga 15 kHz output.
