You might gain 1-2 hp. Maybe 3-4, but not a lot.
A full exhaust is worth 15, or so on the older bikes. I dont see any reason the 14 would not be similar?? Well,, they did change the cam and it was supposed to make the midrange stronger. That may hurt its top end potential???
The move, if you own a 14, is to beg Ivan to do a reflash package for it. He did my 2012, and power went up dramatically. Especially where Kawasaki had restricted it , down low. With a header and slip on, mine felt fast.
Once he reflashed it, the low end became almost terrifying. You soon learn the throttle is best respected in low gears and low rpm. It hits, down low, like an mx bike.
I dont think thats available without a reflash????