2015/2016 Headlights fit a 2013?
 

They seem awfully close, and they look a lot better. Anyone know for sure if they fit the pre-facelift S8?

I doubt it, they are just different enough that even if it could be affixed, there would be unsightly gaps.

No. The 2015 fascia refresh also included a new hood and new fenders.

Hood, grill and bumper surround are different which kind of suggests that the headlight unit is, more likely than not, also different. Probably won't fit a pre-facelift car.