Mixing 2D and 3D

Hi all. In my current game, I made a front screen with a nice fade in/out button made with quads in 3D to use alpha blending.
But after this part, the rest of the game is all in pure 2D directdraw. Some testers are experiencing slow-downs on some systems.
If, after my main screen (which I initialized with graphics3D), I switch back to normal 2D (using Graphics) I may get better performances?

Thanks for the help :)