There were rumors swirling around that Ben Affleck got injured while on set of the Batman-Superman movie. and so when Warner Bros. announced they were pushing back the movie from the summer of 2015 to summer of 2016, everyone thought that the rumor was indeed true. Apparently, that is not the reason they decided to push back the release date.
Warner Bros. said in a statement that it needed to move back the date to allow “the filmmakers time to realize fully their vision, given the complex visual nature of the story.” They also said that they will put an untitled Peter Pan film in the same slot that the Batman-Superman was schedule to release at.
I still think the rumors regarding Affleck being injured might still be true, since they pushed back start of production by couple of months. Hopefully, they do make a good film in the end considering they have more time to make a truly awesome flick.