After upgrading a Team Foundation Server 2010 environment from a customer to Team Foundation Server 2015, we noticed an enormous spike in CPU and memory usage on the database server.
When we drilled further into the issue, we saw the same SQL Server statement being executed over and over again:
On the MSDN forums, we found some more information. This is a bug in the TFS 2015 upgrade process that only seems to exist when you upgrade from TFS 2010.
A SQL script is available that solves the problem, but the issue is also fixed in TFS 2015 Update 1. So I would recommend that if you have this issue, upgrade to Update 1.