If the fridge is the CF 18, it requires 3.1 amps while running. Assuming a 50% running time/day, that is 3.1 amps * 12 hrs ==> 37 aH per day. You have less than half that available in your 15 aH battery. If the battery is lead acid, you should not draw it down more than 50% or about 7.5 aH.
You likely have enough solar panel for your needs but insufficient battery capacity. Try a battery of above 60 aH as a better match.
You don’t mention the current handling capacity of the charge controller, but it should exceed the current supplied by the solar panel.
This is a simplistic analysis of your situation but points out that at the least, you need more battery capacity. Keep in mind that your solar power needs to supply The 3.1 amps of the fridge plus enough more current to recharge what was used the night before in the amount of time the sun is shining full on the panel. The time available is shorter in the winter And shorter still in overcast or rainy conditions.
A battery monitor is also a good addition so that you will really know the state of charge of your battery.
Paul
I thought getting old would take longer.