Right first job unscrew or remove the bleed valve asap.

Then take the car to the nearest tuner and get them to set the boost back to 8psi.

If it ain't chipped and you are running 15psi theres a chance that the fueling is not matching the boost pressure, this will result in running lean increasing the chances of detination ,
which is a bitch if you just purchased the car as you don't want to have to rebuild it yet .

There was a topic running about these bleed valves they are ok aslong as they are set by the tuners when a chip upgrade is fitted and then left alone.