What do I think about the 14" tires? Well, you know what I made them do to
my 2619
If your 2619 has the lift kit, THEN it can almost certainly handle the 15" wheel. (Not the expensive recessed-lug-nuts aluminum one, just the normal stamped white steel wheel, like I've got. This wheel is readily available all over the place, darn near anywhere which sells trailer stuff.)
Without the lift kit, you definitely won't have clearance for the slightly taller 225/R15 tire. And of course, you'd need to replace all 3 wheels and tires. That's a lot of $$$$. But, if you look at the notorious "More Marathon Tire Failures" marathon, (er, AKA "Thread"), you'll see that a lot of smart people DON'T LIKE riding around on the R14" Marathons anyway. Some have done this upgrade, just because of the "running at maximum load" TIRE issue.
(Although it causes issues with the wheel well cover, at least for RockyMntRay. I don't know if maybe he didn't have the lift kit, and he's doing/already done a quick replacement of wheel well cover to resolve the issue. No problem on my 2619, but I've got the big axle, not just the big wheels/tires-- my layout inside the wheel well isn't the same, because the arm on my Torflex doesn't have as much "give" and also because it starts out with a lot more height between the wheel and the body. I don't have the lift kit, the "bigger" Torflex already makes more "lift".
Maybe PM RockyMntRay, or make a new Thread which gives him a holler? He's done it, YOUR WAY, with the 15" wheels on the 3500 lb Torflex. And at the same time you swap the wheels, you could maybe also do a bit of "wheel well conversion" (i.e., the metal lining) plus stronger "mud flaps", or actually extend your metal wheel well liner to BE the stronger "mud flap" (protecting the toilet plumbing and dump valves).
As I've already said, the standard HDWL, exactly as it comes, seems to go into one of the 15" wheel cutouts nicely enough. Having looked a second time, the exposure doesn't seem adequate to attack either the wheel cutout or the lug nut.