Here are a couple of SMD marking code PDFs. There can be a lot of different components marked code 15. You will need to determine if the size/shape of the component matches and check the manufacturers PDF to insure it is the correct one. Knowing the type and size/shape of the component makes for a good start. Start by eliminating all that are NOT diodes and then those that are NOT the size/shape of the component. Then work with the rest looking for clues such as logos, date stamps, etc. The SMD components marking codes database - Starting with '15' (yooneed.one) Catalog.PDF (electroschematics.com)