An external wastegate on your 2015 STI is superior to any internal wastegate setup and will hold boost rock solid. External wastegates allow for quicker spool because they do not cause turbulance in the exhaust stream and also give better boost control. Typically an external wastegate setup can free up 10-40hp depending on your setup. The uppipe uses 14 layer 304 stainless steel and a triple layer flex section for a seriously durable setup. The uppipe comes with a high temperature ceramic coating option as well to keep heat at a minimum. This is hands down the most heavy duty and highest quality kit on the market and includes everything needed except for the wastegate itself.