Personally, I think that the Udemy affiliate program is not worth joining. The 15% commission from low-priced courses will earn you only a few dollars per referral. If you don’t have decent website traffic, you cannot expect to earn much. 

Even if you have a website with decent traffic, I still recommend not to join the program. Instead, create a course yourself and sell it on your website. You can earn much more selling your courses than promoting courses on Udemy.