Despite several years of development time, and that's only in respect of this particular iteration, Warner Bros. still aren't ready to pull the trigger on Justice League. Indeed, any sort of forward motion on the film may have stopped entirely.
In Variety's new piece on power shuffles at the head of the studio they say:
Warner's top brass has indicated that they are awaiting the results of Man of Steel, which opens June 14, before moving further ahead.Note that they say "before moving further ahead," not "before giving a green light." This would mean no interviewing or auditioning let alone any kind of pre-production of more concerted prep. That's if we can take Variety's report as to-the-letter accurate.
The proposed 2015 release date for Justice League probably isn't impossible, though it is looking increasingly ill advised.
My gut feeling is that Man of Steel is going to be a smash though, of course, nobody knows anything.