I went to do an upgrade of TFS2015 to TFS2018.2.
In past tests and experiences, these upgrades take some time against the collections if they are on the larger side. I first started a POC with TFS2015 to TFS2017.3 and that took 24 hours total to do the upgrade and it was successfully completed. As I was doing the POC TFS2018.2 RTM, so I went with the same POC but this time I went from TFS2015 to TFS2018.2, that upgrade only took about an hour or so, which seems really odd.
It looks like it completed without error but the amount of time it took to upgrade the collections seemed really off, compared to any other upgrade I have done in the past. How long is the upgrade process expected to take?
The length of time to upgrade the collections depends on the amount of changes made to the database, and which tables changes were made to, and the size of the team project collection databases.
I recently performed an upgrade against a 500 GB collection from 2015 to 2018 and the entire upgrade process took 20 minutes. It's fast.
Previous versions to 2015 were slow because TFS 2015 introduced significant database schema changes. Nothing after that has required such a major schema change.