15v to 3v LED - resistor vs regulator
I want to add an LED to the power switch.


Any linear regulator or any resistor will "lose" the same amount of power when dropping a higher voltage to a lower voltage. If the input voltage is 15V and the output voltage is 2V then the power dissipated as heat is 13V x current. If the current is 20mA (standard red LED) then the power given off as heat is 260 mW. If you are happy to dissipate that power to activate a LED then a resistor is by far the superior choice because it current limits the LED naturally.