Overload any tire and it's a roadside inconvenience waiting to happen. LT tires actually are rated for less weight than the same size ST tire, so it's important to do the math, weigh your rig, and the get the right size tire for the weight it is carrying. Not all LT tires are rated the same.
If you look at a 15K 5er, 20% of that is on the pin, so 12,000 on the axles, or 3000 per tire, not a lot for an E rated LT tire. 245/75-16E is rated for 3042 and 265/75-16E rated at 3400, etc. Many 5ers that heavy are triple axle. Pick the right size to carry the load.