Certain monitors that.....
1) support the refresh rates of Productivity modes (no scan doubler needed, Amiga games that force the native screen modes to operate, will not display.
You could use a scan doubler, to force 15khz up to around 31khz..
but you still need a monitor that supports..
31Khz Horizontal, 50Hz Vertical. (*ALOT* of monitors do not go down to 50Hz Vertical).