Is the metal top stamped with any relevant information? If it matches that would be good enough to convince me.
Normally I'd assume it was yet another modern fantasy piece, but the etched Bradford seltzers of that color and style seem to have a rather large presence in the search results, and only in blue it seems. They are also referenced in a couple Coke books too.
Since they don't seem to show up in other colors or styles (as one might expect with someone nowadays using the same stencil on whatever different seltzers they could find) I'd say it looks promising and for 15 bucks it is a worthy gamble. One just sold for 130.
And regarding the 15 dollar price tag, well, if the seller forged the item (or bought the item from the creator) I am positive they would be asking well more than what ya paid.