If you change tire sizes, you will need a new 15" wheel with the same lug pattern, of course. The pattern is called "5 on 4-1/2", and it is very common. Be sure it is rated for at least 65 psi.
For lift kit installation, check out Bill Miller's article in the TM Tech Library
https://www.trailmanorowners.com/for...ad.php?t=12132
Strictly speaking, if you are upgrading the tire size, you don't have to upgrade the spare. If you have a flat and need to put on the spare, you probably won't be traveling very far before you want to fix the flat. Driving without a spare is unnerving, to me anyway. The TM has no problem with mixed tire sizes, so if you have a good 14-inch tire and wheel, you can save the cost of replacing them. One other advantage? Although a 15 inch spare will fit on the rack intended for a 14 incher, it is quite difficult to lift the rack into place.
Bill