The only downside when I did it was that the 15" tire is a bit wider, which makes it harder to fit on the spare tire rack. My solution finally was to modify the rack a bit, as shown in Post #4 here
https://www.trailmanorowners.com/for...ead.php?t=5828
Others have done similar mods. And some have taken a different and easier approach. They buy two 15-inch wheels/tires and mount them on the TM. They keep the best 14-inch wheel/tire on the rack as a spare. The reasoning is that if you have a flat, you can replace it with the 14 inch spare, and run with one 14 inch and one 15 inch tire until you reach a tire repair shop. Since the TM does not have a solid axle, it doesn't care if one tire has a radius a half inch larger than the other one. And the flat tire, being flat, mounts on the spare tire rack easily, where you carry it until you reach the tire shop.
As they say, you pays your money and you takes your choice.
Bill