Most likely you will be fine with the 15Amp circuit.
When you first start up the motor there is a current surge in motors (because the motor windings more or less look like a dead short) until the rotational speed comes up so that the back EMF (Electromotive Force) comes into play ... to increase the motor impedance. Once the Back EMF is determining the motor impedance it does not draw as much current. Normally this only takes a fraction of a second, or so, and in this time the circuit breaker does not get "hot" enough to trip. So your 15amp circuit should be fine provided you do not have a large load on the motor during start up... and that you are not trying to run something else on the same circuit at the same time. Normally the large load is just during the startup, to build up the rotational inertia of the motor, gears, belts, chuck etc. plus the friction of the moving parts. After the motor is spinning the current flow decreases as the inertia has been established and the back EMF is large. ... and the only time you will actually use the 1.5HP is when you are cutting a very heavy load at a large radius.
On the other hand if all hell goes wrong and someone jammed something into the machine and stalled the spindle/motor then the breaker should trip! ..... I suppose you could call this a safety mechanism, but not much of one! Anyway, the breaker is there to prevent the wires from getting to hot and catching the building on fire! This is largely dependent upon the insulation on the wires and how close they are to flammable materials. Electrical codes are for safety. You can hook up a big wire to a small breaker, but not the other way around.
I once hooked up a 1HP compressor to a 15Amp circuit breaker. The compressor would start fine and fill the tank with air. However, when it cycled and but the tank was still largely still full (still had most of the pressure in it) then the motor had to start up under load. Sometimes it would start, and sometimes it would trip the breaker. I checked and I did have 12 gauge wire and so as
@Eddyde suggested I swapped out the 15Amp breaker with a 20Amp and all went fine from then on. Later I purchased a 3HP compressor so I could paint my car and so I ran a 20amp/220V circuit.
As an aside story: My 1930 house was originally wired with what is called Knob-and Tube (not Romex insulation). The current feed wires are individual from the return wires and only come close together at the appliance outlet or light fixture etc. The wires were only wrapped with tar and cloth. However, the wires are strung around (knobs) and through (tubes) ceramic insulators and never touch anything that could burn. Hence, my house was wired with 14 gauge wire. These wires were fused at 30Amps. (both the feed and the return are fused as either maybe shared with other circuits.) I am sure the wires got hot and voltage was lost along a wire that was long, but it met code! They were safe. Nevertheless, most home owner's insurers will not insure Knob and Tube any more. I tore them all out and rewired the house. Most of the new circuits are 12 gauge Romex, but 14 gauge is more than sufficent for most lighting circults... especially since the newer LED bulbs are replacing the old energy hogs.
Dave L.
