Here's Featurefilmcasting.com's page back in October 2012...
http://www.featurefilmcasting.com/se...&max-results=2
On that same page, they also list CATWS casting for shoots beginning on March 1, 2013. Anthony Mackie just told AICN that they would start shooting on April 1; so if featurefilmcasting.com has a margin of error of +/- one month, I'd say their info on Ant-Man is pretty solid.
Here's where latinoreview got scoopage that Ant-Man is supposed to "step into Marvel's London production branch once principal photography on 'Thor: The Dark World wraps.'"
http://latino-review.com/2012/07/30/...london-thor-2/
And that came hot on the heels of Simon Pegg tweeting about World's End finishing up and Ant-Man shooting in 2013.
And yes, all this came before Marvel gave Ant-Man the late 2015 release date, but as of yet, there's no indication that Wright has changed his plans for Ant-Man at all. Maybe we'll hear something from the horse's mouth soon one way or the other, but otherwise, there's more solid evidence that Ant-Man *is* shooting soon than there is evidence against that. Feel free to provide linkage to prove me wrong, though.