I think 15 horse is substantial, and will be installing newer headers with high flow cats, and a dropped rear muffler from a complete 2000 system, hopefully next week if the cats come in time.
All told I am hoping for 35ish more horse for this on this el cheapo setup (under a thousand bucks cdn), with a weight savings, cooler side sills, and better sounding car.
Save the big bucks for a charger in my book, multi-thousands for headers is a little steep, better bang for the buck to be had elsewhere.
Then again I am a cheap Canadian.......