I am not a customer of hortonworks/cloudera, just a community member. Is access to the latest HDP stack 3.1.5 given to customers only or can community members get access to it as well? I tried using my community account to download the repo, but have had no luck so far.
I'll refer you to the Cloudera Licensing Policy FAQs.
If you have further questions after reading the policy, you can use the contact us form page to contact sales.