We have Tfs 2015 update 3 on-prem, however, we can't see the task group options in release management. Nor can we add artifact aliases.
Are these only in VSTS? The documentation at https://www.visualstudio.com/en-us/docs/release/author-release-definition/understanding-tasks suggests they might be in both?
Task Groups will be shipped with the next release of TFS i.e. TFS 15 ( not 2015 ).
The RC2 version is available here.