You can. However there are effects on speedometer and odometer.
Punch in those numbers
@ the Miata garage to find out exactly how off each will be. In general, it's best to keep the overall diameter/circumfrence the same when changing tire size. Like, 225/55R15 wuld be a lot closer to your stock size. However, I would not gaurantee that a 225/55R15 tire would fit on your rim on your car.