No unfortunately this is not true. The poster is a mock up by thearnoldfans and, despite websites reporting to the contrary, was not at Cannes. In hindsight it's just as well. I mean, that headband- really? The photo of Arnie is obviously from ESCAPE PLAN with the Albion version of the Atlantean tackilly photoshopped on.
Arnold is currently filming TERMINATOR V, making any plans for LEGEND OF CONAN to be released anywhere near the December 2015 mark highly unlikely. That is if he starts shooting Conan straight after TERMINATOR V. With no script officially in place, no director and the movie not even been given the greenlight as yet, this project is not even as close to production as Milius' CROWN OF IRON was.
It's all down to Arnie.