A recreation of Sonic Advance's special stage really shouldn't have much lag at all. All you would really need to do is have the art for the main stage animated and put it onto Plane A, with the star background being on Plane B. Then, you'd just need a custom player object that could freely move around, a way to handle objects coming towards you, etc etc, and you should be good to go. It's nothing fancy, really. Well, the problem with the example you listed is that Sonic CD's special stages on the SEGA CD use the special on-board ASIC graphic processor to create a 3D effect. The tech demo of a port to the Mega Drive doesn't have that luxury, so it's obviously going to be slower.