No problem! I towed an MKT-85, which is on an M103 chasis, at those speeds. I’ve also towed M105s at highway speeds.
If possible, pop the little hat and get a look at the grease. You might at least jack each wheel up and see if it spins okay. You could easily have a stuck brake shoe.
If the trailer is old, you might need to do a service job on the bearings, but at least get a look at them. It only takes a Phillips screw driver to get the cap off. If you wind up greasing them, put between 15 and 25 ft-lb of torque on the nut.
Whatever you do, stop after 10 mi. of highway speed and feel the brake drums for heat and the little cap over the bearings. If you can’t keep your hand on the metal, you have a problem.
If you go to tow it out of the yard and the wheels won’t turn, look and see if it has a small air tank. If it does, make sure it is empty. That tank sets the brakes through the relay valve when air is lost on the emergency line.
Good luck.