This didn't work as expected. In the first test run, the fan burned up and the 15w resistor got very hot. In the next test, I achieved the ideal fan speed by connecting 3 of those resistors in series. I have no idea why it could be off by this much, but, the supply that I am tapping in to is 19V, 3.42A
I used 15 ohm 15 watt resistors, three of them to get the fan speed I wanted. I think this means that the fan is operating on .42A, not far off from the manufacturer's specification. But using 3 resistors to achieve this result seems excessive, and they take up too much space.
So, to specify some details I didn't mention before, I need to step 19V, 3.42A down to 8V, .38A (at or around)