Why do you even need an ESC? If the motor you are using is rated for the voltage of the battery you are using, just use a switch of some type. DimensionEngineering makes one. An ESC would certainly work though but it would be on or off (no variable throttle needed).
Getting 1.5v might be a little tricky depending on how much current a glow plug pulls. I assume it is at least 2A, so a linear regulator would get pretty toasty by itself. You can use a pass transistor to handle the current and power dissipation, but still inefficient and the heatsink would be fairly large. Same idea about using a power resistor to drop the necessary voltage, but that too would get hot. You could get fancy and use a 555 timer and a switching transistor to make a rudimentary switching PS; just figure out the duty cycle based on the supply voltage you're using (2s lipo would need about 17-18% duty cycle to get ~1.5v). Then again, the glo plug won't be on very long, so I dunno. I'm probably overthinking it again.
