TFS2015: what rights in a collection does a release approver need?

TFS2015 u2. I'm editing a release definition, assigning approvers for an environment.

I have several server-level groups. When I start typing group names in the "Specific users" box on the Approvals page of environment properties, one of them ("Application Hosting Team") comes up, another ("QA Team") doesn't. The former is a part of collection admins, the latter has no specific rights. If I grant the QA team collection admin, it comes up, too.

Question - which rights do I have to grant (short of admin) so that TFS considers it eligible for approving releases? Preferably on collection level.

EDIT: Adding the server level group to "Project Readers" will do, but I'd hate to go through all the projects...

Found two collection level ways:

• Create a collection level group, add server level group to that one, grant Allow for Edit collection level items
• Add the server group to "Release Management Service Accounts"

Either works. The former is slightly more work, the latter might grant more rights than strictly necessary to approve releases.