pv7

I have bought a project Audi a5 that lacks power and there is a rattle noise coming from the engine.
Previous owner told me that the chain tensioner had given out and he had had that and the chain replaced, however after the mechanic changed that, the car was significantly slower and was hard to start.
It has the fault codes P2015 and P0016.

I am new to Audis and would appreciate any help diagnosing the problem