It is your choice, but 68º is a very very low temperature to achieve with residential A/C. Many people live with a system which would never achieve that.
You could get a portable air conditioner which would connect its hose to that small window.
Have you checked the humidity in the house? I know it is humid in FL, but if you have the A/C running that strong, it should be lowering the RH. If the A/C is overpowered, it could be short cycling, which will not get the humidity down like it should.
You would find a better comfort level by lowering the humidity.