From my reading of tire threads, this is what I gather....
16" tires give you more tire options and you can purchase tires with a higher load/weight capability. However, it is common for the trailer manufactures to put on axles that don't have extra capacity -- frequently they are sized to the trailer weight with no extra wiggle room and the tires are sized to the trailer weight with no extra wiggle room.
Prime Time does sell the 16" upgrade on the Crusader trailers. I wish I would have done that to have more tire options.
Now, having said all of that.... I researched this to death because I'm concerned as well about the tires that PT used.
The most recommended tires on the forums in 15" are the Maxxis M8008. Down side, speed limited to 65 pmh.
The ones I will probably try when it comes time to change tires will be the Carlisle Radial Trail RH. They have a new design that addresses the problems they had a few years ago. Also, they have designed and tested this ST tire for a speed rating up to 87 mph (depending on the size you buy). It's the only ST tire I've come across that has a speed rating above 65. People are starting to make positive comments about the new design (about 3 years old now?).
If you want to go with larger rims and go to an LT tire, the ones that get the most recommendations are the Goodyear G614, the Michelin RIBS, and then to a lesser extent the Sailun S637 and Bridgestone Duravis R250. (I think those are all LT.) I've read that the G614 will provide some warranty coverage for RV repair if it fails and damages the RV (you must keep the tire and ship it to Goodyear).
2014 Crusader 296BHS
2015 GMC 2500HD Denali