We have the 2015 GT 364TS with the 19.5" wheels. I talked with FR last week and they said it came from Ford that way. So, I called the lead MH engineer at Ford. She said that's how FR ordered them! So, who knows? I've wanted to switch to 22.5"s for a while. Be aware the 22.5"s do not fit the 19.5" wheels. The bolt pattern is different which means you need a different axle hub or a completely different wheel design. On IRV2.com, there is a guy "Lvrvluvr" who is selling a set of tires with wheels that will fit for $6,500. (But, I was told he bought them for $4,500.) If all of that isn't enough to swallow, throw in the fact that the Ford engineer said they get about as many complaints about sway with the one size as the other. Still, I'd like to make the switch, but it's more economical to just live with it. By the way, the XL has more than just different tires, e.g. two water heaters. The 6-speed transmission is a big plus. Wholeheartedly agree with RVnut, get a 2016 or find a 2015 XL. Don't let the dealer pressure you if that's not what you want even if you're close to signing the papers.
2015 GT 364TSF