I use Mac OS 10.12 and Lightroom 2015.7 CC.
My catalog file, unzipped is 1.5gb. Lightroom refuses to compress it with a note that it can't compress files over 4gb.
I just saw this for the first time after upgrade to 2015.7 CC.
Please read here: Lightroom catalog backup issues after 2015.8 update
Retrieving data ...