I wonder if they might be doing something with MB's AMG division considering they have agreements in place for engine & platform sharing.
They could do a different version of the engine going into the 2015 C400 with some more ooomph.
From the sound clip, the startup of the engine definitely has a turbocharged burble to it, not to mention the blow-off valve sound on throttle lift off. It also kind of sounds like a manual transmission with the delay in shifts and the blow off valve going off between shifts.