your board size is fine. ive found board size to be more personal preference then a designated thing. if you find it hard to turn and overwelming its probably a big and if its really unstable at high speeds its probably too small. it depends on the type of riding you do really but 159 is a good length for an all mountain board, you might want something a bit smaller but i wouldnt waste money on a board upgrade unless you need it. park boards are short, powder/high speed boards are (typically) long, anything in between is usually all mountain.
im the same height as you and when i was around you weight i was riding a 157 burton air and it was perfect. with my bindings set back i was able to ride very deep pow quite well. im fat now and i ride a 163 salomon powder snake. i usually prefer a bit smaller board but its not a big deal.