basically, from wat i get out of the description.... it increases the rate at which fuel is sent through the throttle body, the ecu would then (in theory) read there is more fuel going in, and increase the ammount of air added....
more fuel and more air = more bang for your buck = more power.
however, it does mean that you will burn more fuel therefore reducing MPH.
there is also the risk of running rich, which will f*ck up engine internals and your CAT.
have a google search for "FSE power boost valve" as its exactly the same thing, should give you more info.
advice: dont bother, u wont get anywhere near 15% increase, and run the risk of doing expensive damage.