How can i run automated selenium tests using TFS build 2015?
If you're using the Hosted agent queue, you can't. If you have your own on-premise build agent, you just need to run the agent from a command prompt (as opposed to as a service). That's all that "interactive" means.
You can also use the Test Agent tasks to deploy a test agent to a target machine and invoke the tests on them. This will also allow you to run UI tests even if you're using the hosted agent queue -- you'll be passing off the running of the tests to an on-premise test agent.
On a side note, you should generally not run UI tests as part of a build process, but rather as a step in a release pipeline after the application has been released to a QA environment. UI tests are slow and brittle, and you don't want your CI process to be bogged down with running UI tests.