There is as of yet no official confirmation that the second series of Attack on Titan has been delayed.
This week, a few reports have cropped up claiming that the second season of Hajime Isayama Attack on Titan's anime adaptation has been halted indefinitely. We have done the research, and were unable to find a solid source on this one, so we're officially declaring it one of "Bogos's boguses".
First up, almost all of the outlets reporting this news don't have an actual source. The one we were able to find that did actually have a source was just a broken link to the "official Attack on Titan Facebook page."
Secondly, a lot of these reports claim that anime director Tetsuro Araki has decided to delay the anime because the manga is not a full four story arcs ahead of where season 1 left off. While this is true (the anime is only three story arcs ahead), the last two story arcs have proven to be considerably longer than the earlier ones in the series. Araki has also not made any official public announcements regarding the series in recent months.
The only official pieces of news we have to go on is the official advertisement for season two you will see in the video above, which aired in Japan this January, and the official press release from Attack on Titan's production company which both simply state that we will see season 2 in 2016.
So the rumors circling around that the second series has been "delayed" are just that - rumors.