Your biggest issue is going to be how much room you have between the tandem axles now and how much that will decrease when you go up in a larger size tire..
I had little 13" wheels and tires on my old 2003 Prowler Lynx.. I wanted to upsize to 14", but found that there would be no room between the tires and suspension travel.
The 13" OEM tires were LR "B" tires... I simply upgraded to LR "D" tires in the same size and problem solved.
See if you can get some LR "D" tires in your current 14" size. That'll likely be better than the "C" and give you that little extra LR.. The bolt pattern of the wheels are all basically the same from 12" to 15" wheels which is 5 on 4.5" bolt pattern.
Good luck! Mitch
