Franz,
As I read your initial post, I think the bottom line of your question is not just whether the piece is difficult, but whether it would be a good choice to learn in 6 months for a shot at playing with orchestra - correct? I would recommend another selection. This concerto is performed A LOT and is recorded A LOT. Your playing of it would be compared with everyone under the sun. Presenting it needs more time than six months to allow your own interpretation to develop. For your audition, I suggest you find something a little less well-known. Have you ever looked at the Shostakovich 2nd concerto? People have different opinions about it, but i love it, and it's not all that often played.