Well your not going to gain 15 hp, so if you thought thats what your going to gain you got scamed.
You would be better off cancelling that and going to get a complete engine tune from Tom or another respectable professional tuner, the O2 sensor only has an effect on the fuel ratio to meet emmisions requirements, this one here is not custom, will have no aftermarket support, cannot change idle rpms, and will not have a affect on timing amongst a list of numerous other "tunable" parameters, while professional tuners will be able to change everything that I just listed and will always be able to provide assistance if something goes haywire.