I think the AmigaKit website is confused. Only a few CRT monitors can do 15KHz. It does correctly mention the screenmode that are supported though (all of which are 30KHz).
To re-iterate, though, this adapter is NOT a scandoubler and games will not work unless they run in workbench and you have an ECS Amiga.
I would recommend using a bog standard Amiga RGB cable and attaching it to an LCD telly, most of which act as a scandoubler internally.
