If all you are trying to do is make an "on" indicator, there is nothing that says you need to run the LED at 25mA. I have run some "ultrabrite red LEDs" on as little as 500uA, and they are bright enough to see in sunlight.
If the goal is long battery run times, then try 1/2 to 2mA, and see if you like it.
The formula for figuring the resistor value has already been given to you. Just reduce the LED current by making the resistor bigger: R = E/I = (9V-2.2V)/0.001mA = 6800Ω. (Resistor range 3K to 12KΩ).
The power rating of the resistor just has to be more than the resistor is actually dissipating which can be calculated as P= I*E = 0.001mA*(9V-2.2V) = 6.8mW, so a 1/4W carbon or metal film resistor is more than good enough.