You can use any sewing machine oil on this machine. Also any low shank feet which are very common and easy to find. Personally, I'd go for vintage feet for this machine, and you can always find them on eBay and Etsy. Just don't get sucked into paying more because they are listed as being for a Featherweight - because all low shank feet are created equal whether they originally came with a 15-91 or any other low shank machine.
You can also use modern low shank feet, but keeping in mind that most of these sold in sets include feet intended for zigzag machines so wouldn't be useful to you. However, you CAN get a modern quarter inch foot for quilting.
The feet that originally came with the machine included: straight stitch foot, zipper foot, adjustable hemmer, rolled hemmer, binder, ruffler and gathering foot. If you're primarily a quilter, you wouldn't even use most of those. In addition, you can get clunky but interesting attachments such as a blind hemmer, zigzagger with decorative cams, buttonholer, and hemstitcher. These aren't really useful to most sewers, but there is a fun factor if you're into that kind of thing.