As most have said above, the weak link in your setup is the tires. My 2013 F350 has a GVWR of 11,500 and I am over that by about 600 pounds but under my front and rear axle weights. Your Lance is much heavier than my Igloo. I have 3,750 E rated tires and I am religious about the air pressure because I am close to their limits. As others have recommended, take it to the scales loaded like you are going camping and then let common sense be your guide. You can do a lot to beef up your suspension but you can't do much about your existing wheels and tires. Don't forget you also have to stop that rig - make sure your brakes are up to the task. After our first long trip with the Igloo I started looking at after market brake pads to increase the bite.
I am not one to lecture about weight - you will do what you will do. Be sensible and safe. Get real weights and look at all the elements in your carrying system.