At first I thought it was, but now I don't think so
Especially in the beginning, the missions don't take very long to complete. But the more I play, the more I think the later missions are just as long as JO's were. I think the difference is that a lot of the time in JO you were running around solving difficult puzzles (jumping and otherwise). This ment that the game took longer because so much time was "wasted" figuring things out. I played through JO a second time and it was much quicker because I knew where I was going. I think JA is just as long as JO, but the first time though you are not spending as much time solving puzzles.
Just my impression.