I've read that screens don't find anything below 50 and that tests will find down to 15 or above, so considering my recent diet and the fact I drink about 8 bottles of water or more a day what would an educated guess at my chances of passing be?
Only periodic testing with a THC test kit (using the first urination of the day) can give you that answer. Each persons body is different and there are too many variables to take into account to arrive at an educated guess.

By utilizing the Forum Search button with the terms "functionally equivalent metabolites", you'll discover that a 50 ng assay screen is functionally equivalent to the 15 ng GC/MS.