Well...thats 20-22volts drop...so thats up to 22x15amp=330 watts of heat!
I think 5-10 volts is max on a 120 outlet depending on who you ask. The older motor might have drawn less power, had internal differences, etc and been less sensitive to the heat.
You should stick to Mechanical stuff.
Your calculation is showing what is being dropped in the wire as heat assuming that all of the voltage is being dropped in the conductors as well.
110-120V is the rating on most.
100feet is too much, because you need to double it because the return path. So you have 200 feet of conductor+ the double the length of the cord as well.
I don't have my NEC book with me to actually get the impedance value/foot of the 12 gage wire. However the next step would be to measure the voltage at the panel when your running the saw as well.
However 96V at the outlet is too low.
Say 115/96 is 1.2. To make the saw do the same work your drawing 20% more current. And we know that current^2*resistance is the power(so your actually putting more heat into the motor to the 2nd power).
Enough rambling.
Measure a few points along the way for the drop and see if you have an issue with a bad connection etc. If you don't find one, and the voltage at the panel isn't dropping much, I would say your best bet is to run a #10 to the saw outlet, or move the saw.
Is this a sub panel, or tail panel off of another service? If so if those conductors are not very large either, you need to figure those as well.