The proper metric tire size would be 225/60/15. They are a bit snug in the spare carrier, but they will fit with a little adjustment on the carrier attachment bolts. At the front of the carrier, there are two long bolts holding it to the frame, that allow it to swing down. There are nuts on these bolts that keep them tight . Loosen the nuts a little then unscrew the two bolts to make then stick out of the frame farther. You can only go about 1 inch. There are holes in the frame you can look thru to see how much thread is left on the bolts, so you don't go too far, and take the bolts all the way out. Then, tighten the nuts back up. This should give you enough room to install the spare. It will still be a little tight, but it will fit. You will also loosen the single rear bolt, the one with the lock. It has(or should have) a pin in it to keep it from coming all the way out, so you'll know when to stop loosening it.
hth