The document reportedly lists not only a Justice League movie but also a Batman movie for 2015. A Justice League movie has long been rumored for a summer of 2015 release date, but it has been thought that a Batman reboot wouldn't happen until 2016 at the earliest.
The timing of the information is very interesting, because DC Entertainment and Warner Bros. will be hosting a couple of panels at 2013 San Diego Comic-Con on Saturday, July 20, 2013. It is almost for certain that Warner Bros. will be announcing a Man Of Steel sequel during their Superman 75th Anniversary Comic-Con panel, but an announcement of a Justice League movie and a Batman movie would be somewhat of a surprise.
It's likely that the Man Of Steel sequel is Warner Bros. next biggest priority, so if Justice League and Batman are scheduled for 2015, then it would suggest that the rumors of a Man Of Steel sequel in 2014 could be accurate. This report should be considered rumor for now, but fans won't have long to wait to find out if it's true, because announcements one way or the other will be made at Comic-Con tomorrow.