The differences between the 2015 version of TeX Live and older versions are far too numerous to attempt to collate. Many differences will not matter for the purposes of this site. Please add any specific information which affects processes on this site below.
This information is specific to version 2015 of TeX Live.
The command ifboolexpr may be relied upon when creating LaTeX (Transformable subset). This command was not part of the original package and is not present in older versions of TeX Live (definitely not present in 2009).