There is a rumor that the first teaser trailer for Batman v Superman: Dawn of Justice may be out as soon as next month. That would seem like a long time before the movie's release date of March 25, 2016, almost too early to do a teaser. But if you think about it, normally a teaser for this big of a film would be released a year in advance, so this would only be a few months earlier.
Also, Warner Bros may be thinking of attaching it to the final Hobbit film, which is likely their biggest film between now and the spring. And a lot of the film has already been shot so putting a teaser trailer together now shouldn't be a problem. But along with the timing of the teaser, it's also said the teaser trailer is done and is going to be a very Batman-centric.
[Source: Batman On Film]