The 150 liter Start Small will certainly work for you if you have some skills, and enough wind.
The newer Start boards (> 2002) do not have the width and volume to make really great beginner boards unless you match sailor weight to board size.
At 185 lbs, the Start M or even the Start Large would normally be considered best for a sailor with no skills.
If you have some skills (gained on a larger Start or perhaps a longboard) then you are ready to progress, and the 150 liter Start will be OK.'
You will need a bit more wind, and a larger sail (than a beginner would need) but the Start S will certainly float you OK.
Hope this helps,