I just checked if there is an announced released date for the 2nd season, but couldn't even find anything about the 2nd season. I found a page saying this:
The production studio has announced 13 episodes of Arslan Senki so far, but the story of an epic legend that is unfolding before the audience continues to be published as a manga, so it is very likely that The Heroic Legend of Arslan will get renewed for a second season. Most likely, season 2 of The Heroic Legend of Arslan will get released in winter of 2016.
The first season is already over 18 episodes and this week we will have the 19th so is there even going to be a second season?