No, by "draw tiles" I mean don't let GM draw them at all, period. Mark (and I thinK Studio's programmers too) messed up tile functionality and it is horrifically slow during the GM's drawing phase. You can use tile_layer_hide() to disable drawing of the tiles but leave them in the room, or use tile_layer_delete(), but in a Castlevania game I'd stick with just hiding the layers.
I don't remember which version of GM you use, but here's a GM8 quickie I used to test out the difference between letting tiles be drawn and just converting the image to a background to be drawn instead.
http://www.mediafire.com/download/61g4o8or7m36ccs/smb3_angry_sun.gmk If I uploaded the correct file, when you run it, press SPACE to toggle tiles on and off. If you're using Studio, you'll need to Import the project. All the code is in object0.
Also, the prisoner probably only takes up 10 or so frames of animation and they just did a better job of coding it than you.
But that would be a RAM issue, not a CPU performance issue. They go hand-in-hand sometimes, but that shouldn't be affecting you too much. ... Although cutting out 15/16th of a sprite might not be bad.