You and I are in the same boat. I've been getting in the 15's for a while, and started replacing things. Try replacing your fuel filter, check your tire pressure, (I know, it's a no brainer, but you never know) Maybe give your inside a good old cleaning with some seafoam. Check your PCV valve, it may need cleaning.
Dual exhaust w/Flowmaster super 44's.
GoodYear F1 tires
17" five spoke GT rims
Painted calipers, Painted pony, flat black painted hood stripe, flat black painted spoiler.