Changing the size of the image will (obviously) make it slower. The bigger the image is, the slower it will be.
Also, Roaming Ralph has no physics. Roaming Ralph only has collision detection.
Perhaps you're making an horrible mistake with your code, which is seeping out performance juice as well.
Anywho, if it was me, I'd try using the 33x33 image and see how fast it runs, compared to the Roaming Ralph sample (taking into account that Roaming Ralph only uses collision detection, so it should naturally be faster) and then compare it with the 129x129 image.
Hope this helps,