What Manalto said. Here's the link to ISMACS' database:
http://ismacs.net/singer_sewing_mach...-database.html
The area around the bobbin case is much smaller on the 115 than the 15. You should be able to find a manual at Singerco.com under resources. They have free downloads for most models. Your machine looks like it's in nice shape. Read the sticky on cleaning old machines and watch Muv's videos. Only use sewing machine oil or tri-flow synthetic oil. Harsh cleaners will damage your decals. If the machine doesn't want to turn, oil it and wait. The new oil will take some time but will soften any old dried oil that's gumming up the works.
Nice get,
Rodney