How to lower wattage of circuit
You have linked to an eBay ad instead of a datasheet. The fan has four wires so it probably has a PWM speed control input on it and electronics to efficiently control the speed  without the high heat loss of a resistor.
Internally the fan is not a simple brushed motor but is a miniature brushless DC motor with a chip generating a three-phase supply to the coils. You will find plenty of reading material on the web explaining their operation.
&quot;No datasheet? No sale!&quot;