Cameron to make two more 'Avatars'

I hope this one is not a rumor, and the article provides quote, so may be there is something substantial.

He said: "I have a trilogy-scaled arc of story right now, but I haven't really put any serious work into writing a script".

James said he hopes the next two films will take a little less time to make however, because 'Avatar' was in production for four years.

He said: "My next goal is to refine the technique, make it easier so it doesn't take as long. We were doing a lot of pioneering work on 'Avatar.' It wouldn't have taken as long if we already knew exactly how to do it."

Source

So, not only 2 more Avatars, but sooner, not waiting for 15 years ;)