Nice! Love those 1915s. I'd guess from the color that it was probably blown at Laurens Glassworks in South Carolina. Look closely around the heel for any lettering.
Here's what I was talking about, a 1915 with "L.G.W. 26" on the heel. This example also has Coca-Cola in script on the bottom. Some have it, some don't. Just wondering.
Update: took a closer look at the base rim...there is lettering that states, very faintly, REED. A little research reveals 1920 manufacture date and explains the vivid blue color.