I cannot make the comparison as I do not have and have never sailed the Isonic 150.
I like the US147 alot.
Getting a new light wind 9.2 m2 race sail soon to take advantage of the US147's light
wind planing capabilities.
I see that your next smaller slalom board is the iS 107.
I think the US147 probably gets going a bit sooner than the iS 150, and also has a better range
so it could be a one board solution for your light wind sailing..