Vintage German Shaving Mug (Lilies)

I know very little about this shaving mug or its origins. I've had difficulty identifying the bottom marking which says only "Germany" (not "made in Germany"), with the number "15" in the center. From what I've gathered, the fact that is says "Germany" and not "made in..." is significant, and makes it an older mug. How old, I'm not sure. Read somewhere it could date as early as 1880, but certainly before 1918 (based on the "Germany" only marking). Would love to hear if anyone has more information they'd like to share. Thanks!

UPDATE: Decided to part with my two vintage German mugs via Ebay (if anyone's interested). http://www.ebay.com/sch/twstack/m.html