Hey Jenn,
Are you sure that's a 115? It looks like a VS (variable shuttle) machine. It takes a long bobbin, right? And it doesn't have a tensioner on the faceplate, I thought all the 15 series had them on the left. I also thought the 115 was a later model, not the 15 mind you.... the long plates and the "Shovel" plate at the top make it look like a VS /27 style machine to me...
This one looks a lot like the 1889 VS2 I have here... only in better shape (yours, not mine) but I'd be interested in knowing if I've misidentified mine...