You installed G614 tires for safety reasons and they should be inflated to 110 psi. Just because your camper weighs 15000# doesn't mean the weight is evenly distributed across the axles. I have a 2016 Cardinal that weighs 14000# dry, but it weighs considerably more on the left side (as opposed to the door side). The reason it weighs more on that side is because the slideouts run almost the full length of the fifth wheel. In addition, cabinets run the full length with a large pantry, all appliances (inc. Residential ref), TV, fireplace, most of king bed and other storage are also on that side. Door side - slideout for dinette and TV lounge, bathroom and that's about it. Bottom line - unless you have weighed the load on each side of the camper and know the weights for sure - inflate to max load rating. I replaced the Goodyear Marathons that came on the Cardinal with the G614 for the same reason, as you. Yes, I run them at 110 psi.
2015 Camping - 192 days
2016 Camping - 129 days
2016 Cardinal 3850RL - 7/31/15
2015 Ford F250 - 6.7L - King Ranch - 4X4 - Air Lift 5000/ wireless air