[Matt55330]

more then likely some numb nut used an impact gun to torque down the wheel some time in the past, easly hitting 3-4x the torque spec even with the smallest gun.

When you torque a bolt you stretch the bolt slightly if you go over spec you take the bolt into a plastic state where the stretch becomes permanent and it's a short trip to complete failure past that.

As far as the comment about needing wheel spacers to avoid a bad joint design, since s-15 came from the factory with steel wheels they already came with the worst case scenario, and any alloy wheel would increase the length of the bolted joint decreasing the stress for the same clamp load.
Also I noticed you were using penetrating oil to loosen the nuts make sure you clean that off prior to torquing, the reduction in friction causes a major increase in clamp load when applying the same torque.

If you want a do a quick check clean any crud off the threads spin the nuts down on the studs. You should be able to do this with out a wrench(at least on the second try). If there is an issue use a thread checker to see if you can spot elongated sections of threads near the base. Those should be replaced now, if they check out the stud is not likely to snap anytime soon.