I'm trying to associate a test run to a release if possible, and if not then a build.
I need to either be able to associate it before the run, or after when we view the history.
I've been looking online and all I can find are references to functionality of 2017 that isn't in 2015.
Is this possible?
It's not possible in TFS2015 for now. You have to upgrade your TFS server to TFS2017updae2. Detail steps please follow this tutorial: Run automated tests from test plans in the Test hub