737 'normal' is to stop at F15
Don't quote half a sentence. What I said was
I do not believe that there is any point in leaving the flaps down for inspection on an A320.
The B737 is a different kettle of fish. The flaps on a B737 hang down behind the wheels, and are double slotted. They do get full of slush.
The flaps on an A320 are one piece and are way up above the wheels. I personally have never seen slush in there, but consider it normal on a B737.