no they won't, the pixmaps are always 32bit, no mather if you have or don't have alpha.
There is no way to reduce pixmap size unless you rewrite the module itself to compress the pixmap (and uncompress it for upload to graphic card to create a texture).
There is no way to reduce pixmap size unless you rewrite the module itself to compress the pixmap (and uncompress it for upload to graphic card to create a texture).