Replacing a 15A outlet with a 5A outlet
If you're intent on replacing the outlet rather than the refrigerator's plug, and want it to be safe, you can replace the 15A outlet with a box that has a 5A circuit breaker feeding a 5A outlet.

You can also keep the 15A outlet and have the above mentioned box as an adapter that connects to the 15A outlet with a 15A plug.