And, actually, EGA timings aren't actually 24 kHz, they're 21.85 kHz.
(Oh, and for the sake of completeness, while I've been saying "15 kHz" for CGA h-sync, it's really 15.734 kHz.)
Now, one of those cheap CGA/EGA/YUV to VGA boards will get a CGA (or 320x200/640x200 EGA signal, but not 640x350...