You're right about it being a Japanese clone and a very pretty one. Billy (lostn51) says the clones are better than the originals. There are tutorials for a complete cleaning, but you probably don't need anything that extensive. Find a free manual online for a 15 and use those directions for oiling, greasing and cleaning. You can remove that pretty plate on the back to get at some of the interior parts. Oil it, sew with it, reoil it and you'll be surprised how much smoother it will run. I got my manuals from sewclassic,com, but the Singer site has them, too. Is it Ismacs?
Post her picture in ther vintage machine thread. She's so pretty, she'll be appreciated.