I know this calculator is a big generalization but it is a great starting point for board sizing. Enter your specs, be honest with your riding ability and what your primary usage is, and it will be fairly close.
Snowboard Sizing Guide, Size Calculator
Based on that calc as an intermediate or expert freerider 156 would still be a little long. Again it's just a starting point for sizing, and other members and I have pointed out that it's not impossible to ride a board that's significantly longer than "ideal" it just would be tougher for a person to learn on a longer board.