Originally Posted by Bama Rambler
I take a different tack than most above posters.
If you're just going to use it as a spare to get you to the next tire place, and not in regular rotation then I'd say it'd be fine. The spring 'equalizer' will adjust to keep the loading the same between the tires on the same side. And the little bit out of level it'll make the RV isn't going to matter.
I wouldn't run it like that normally, but as a spare, it'll be fine.
Agree, using the slightly shorter wheel/tire combo for a spare will be fine. One inch difference in aspect ratio (overall height) is only 1/2 inch of mounted height.
Make sure your upgrade to 15"s has 0 offset so as not to affect bearing wear. Maybe take it one step further and carry two spares of the same size then simply change both tires on the same axle and the equalizer will compensate just fine.