I have been able to trace this to Munich. It appears to me to be the numbers 1 and 5 or 3 suggesting the 13 or 15th year of a century. The only resource I can find suggests these markings used throughout 1600-1800s. Apparently the date numbers started in the 1700s. But I cannot find any details on which monk marking corresponds to which time period.
Also cannot find any details on the maker. The initials appear to be BM.
There is very little information available about these old marks. If anyone knows, can you also direct me to a resource where I can self help myself a bit more in the future? Thanks!