over charging

13.8-14.7 is pretty normal, 15V is not especially worrying. My 2012 Cruze occasionally charges at 15.4V if the battery accepts charge, when its cold out.

I would ask if you are measuring at the back of the alternator or at the battery? I think you should give us readings from both.

Typically the sense wire is trying to maintain a voltage at that location which can be largely effected by the condition of wiring or connections. That and the OE regulator has to have a good ground.