@Thomas Oddly enough I agree with you.
Maybe I asked the wrong question. Some Warp3D games want the video mode in 15-bits and people do get them to work with voodoo, so how?
Maybe they are promoting the video to 16-bits? like Nightlong
So how do you then promote to 16-bits?
Don't have my Amiga with me and can't really remember if I ever used 15bit on my voodoo.
A great utility though is this where you can force some screenmodes to test.
http://aminet.net/package/util/cdity/NewMode_V39