I was googling a bit and what I could find was that there is something called besonders leichter Fall and something called leichter Fall. Drivning more than 15 km to fast "Innerorts" is Leichter Fall and would mean Leichter Widerhandlung, i.e. you lose your license for one month.

So it seems to all come down to how accurate the camara was mesuring your speed. If they give you 5 km "grace" you should be fine.