My advice is to check em with your hand every time you arrive at ramp or back at home. Then you know how they should feel. Mine (single axle + disc brakes) get a little warmer in the summer, or when the tow has a lot of downhill such as going into guntersville and up and over to the state park. They NEVER get hot enough to be uncomfortable to touch, not even close. Only thing to watch with brakes is when you replace the pads, be sure that the piston retracts easily. Since disc brakes are always in contact with the rotor, the caliper piston is extended a little more each time as the brakes wear. A little water will cause some rust spots, and new pads will make you push those rust spots back into the caliper cylinder where they wont move as easily. if you are towing on level ground, 150 sounds hot unless you are measuring the rotor itself. Many IR thermometers have a pretty wide angle of input and can measure temps significantly away from where the laser dot says. Not all, but many.
.
