Gator,
If you don't have the book, The Practical Book of Cobs by Daniel Sedwick, I'd suggest you buy it to assist you with ID-ing cobs.You may also find it worthy to check his company's online site and review prices received on similar items that have been recently been auctioned off.
Don.....
Sorry, Gatorboy, but there won't be much additional information to garner from such a specimen. There is no peripheral legend. You have already mentioned it's provenance as originating from the 1715 fleet. That is probably as good as it's going to get. So in summary, a Mexico City 8R minted during the reign of King Philip V with provenance to the 1715 fleet.