Trouble with color depth!!!

Hi All!
I have some trouble with my app.
When I try to run it in 16bit color it looks very slow (about 1.7 fps), but
if I run it in 32bit color it’s ok (~33fps ).
My program uses MFC.
Maybe I do something wrong with PIXELFORMATDESCRIPTOR?

Are you using the stencil buffer?
I think most cards supports hardware stencil buffers only in 32bit color.