I have seen one that was done like that, and it will make it look funky. The tires for the 13 inch wheels may not have the load carrying capacity needed for the car. I would also worry about the shock end hitting the ground before the wheel in case of a flat, because a two inch drop spindle will allow the shock end to hit the ground before the rim with a 15 inch wheel. As above, the front wheels may not fit over the brakes, but you could put spacers behind them. The rears should fit, because the drums are only about 12 inches in diameter. I would worry about the load carrying capacity and interference of the shock ends before anything else.