Fridge draws less than five amps running. You have 15, no damage.
Also.. This is the important thing here.. The major power sucker in the firdge is a resistor, the other things that draw 120vac basically draw nothing, they only look to see if there is 120vac there or not (The detector that switches you to electric).
Low voltage (The danger when using an extrension cord of the 15 amp variaty) will NOT DAMAGE a resistive heating element. (Think light bulb).
It will, however, tear up a motor (Think air conditioner) big time.
Home is where I park it!