Yes, I've got a whole army of 15mm fantasy figures (although I haven't painted or used them yet), and Luke's recent video is familiar. I'm pretty sure I've seen someone on this forum showing off their version of downscaled Warhammer/KoW, years ago.
There are many ways to go about with this. Some halve everything and reduce the 20mm base size to 1cm x 1cm. Some just put more minis on the base and enjoy the increased feeling of mass and the realistic proportions of terrain and the huge size of the monsters, but otherwise play in normal game scale.
-Z