I'm trying to install Test manager extension for my TFS 2015. I'm admin and was able to get/download Delta copy extension from marketplace without any issue but not able install Test manager. It says -
We did not find an organization for which you are an owner or a member.
Test manager provision can be used directly in TFS 2015. Please set/change access levels for your account to Advanced. I suppose currently your account might be listed as basic, check your access level as follows:
Change the access to advanced, you are automatically provided/entitled with Test manager provision. I found this article over here