Hey Man,
The stays in the 2015 are going to be a little wider, but not much. If you can pick up a 2014 for a good deal, I would do it. I never had any issues with the TB 2.8 tires mounted on the WTB i45 rim. I liked the extra width of the rim and how it gave the Yelli a softer feel in the back. Awesome combo.
If you need a wheelset for it, I am actually selling my set I had on the bike. Blue Chris Kings laced to the WTB i45 rims. Normally $1000, but I would let them go for $750.
Just throwing it out there. No pressure, just a fyi.