Just thought I would add this:
During the in place upgrade from 2015 to 2016 we have run into some interesting issues.
Environment: 2 servers running as a load balanced pair behind an F5
When we went to run the upgrade on the first server, we got an error that said :
"Unable to connect to orgname_temp db."
This DB does not exist.
But that's ok, because then we hit ok, and setup continues.
You can step through the entire setup process, and when it runs the validation checks, it will error out on connecting to the orgname_temp db, which really, isn't that surprising seeing as that DB DOES NOT EXIST...
As long as you have added the ignorechecks registry entry, the setup will allow you to continue.
The install will start, and then partway through that one, it will error out with
"Setup has detected files in use. Please close the applications that are using..."
Abort, Retry Ignore
So we ignored it. Like you do.
And then we got another just like that.
So we ignored it too. Like you do.
Setup then continued and finished.
Reboot, and we were able to get into deployment manager, so we added update .01 before updating the Orgs.
Started the update on the 2nd server, which had been getting the same error of "Can't login to orgname_temp db"
But now, it didn't get that error...
All the same steps as above, including the ignore, ignore.
So now we are ion the process of updating the Orgs.
If anything untoward happens, I'll let you know.