If the file
release-texlive.txt in your TeX Live 2015 folder , e.g.
C:\texlive\2015\release-texlive.txt, is missing, use this file:
At the time of my writing, the content of this file is:
TeX Live (http://tug.org/texlive) version 2015
This file is public domain. It is read by install-tl --version, tlmgr --version, and texconfig conf, and a final line appended with the precise version number by tl-update-images during a build.
The following blank line at the end helps avoid confusing output when used directly from svn, so don't delete it.
I found this solution after reading this message by Adam Maxwell.