I don't think you can use the SALE code on top of the 50% discount cuz when I tried that it adjusted the 50% discounts so they weren't really 50% anymore..in the end it was still only 50% off after stacking the codes.
It takes 15% off FIRST then does 50% off of that total. So if something is $100, it subtracts $15 which totals $85 half of that is $42.50. That's still more than 50% in the end. It's 57.5% to be exact. haha.