If the monitory really does sync to 15KHz, all you need is one of
these. It's a straight-through electrical connection, just a change in the connector shape.
There are older monitor adapters like the famous Commodore silverbox and the SyncStrainer - these have some extra circuitry in them that you'll need for the Video Toaster and maybe some other advanced professional video hardware. But for regular usage, the adapter linked above should be fine.
Since it's 15KHz capable, most things from from Devs/Monitors should work. stevee617, another member here determined that the Dell SR2320 was also 15KHz compatible. I picked one up and did some testing on all the native Monitors drivers. All the important ones work, with some caveats for unusual overscan situations. There were also some Benq monitors mentioned in that thread -
here it is.
Good luck, and please report back with your findings!