Which QB do I need to learn QB 2015 for my online class. I have QB Simple Start and it is not the right one

Anything with a year in the name is desktop version, locally installed on your computer and QB2015 is obsolete and was no longer supported as of 5/31/18, two years ago. If someone is selling you a class on QB2015 and not QB2020 then I would say it is a scam. Ask the instructor, in fact the syllabus should have identified the proper product - most of the time classes like this provide, for a fee, the correct product license

What you bought is an online product only and is not sold by year.