this is spanish silver and would normaly have a pentagram or something else beside it but could have been rubbed of through use.
is that a real pearl? Nice find, the tube (or trombone) clasp most likely indicates it was made in Europe from 1890s through 1940s. I vote 1940s.
I'm not sure what the 915 means, but that is stunning, if you plan on listing it will you please contact me with the listing number. I'm a sucker for brooches, I have metal allergies and can only wear brooches or a necklace long enough to go under my collar.