It's always a very difficult question to rate/compare planing thresholds, especially at the super marginal planing end of our sport - simply because there are so many important variables that we can't isolate, evaluate or control from our side.
So (for purposes of discussion) everything else being equal - and it never is - the F162 in FW trim will plane about 1.5-2 kts earlier than the iS150. That doesn't sound like much, but of course at the very marginal end of the wind range around 6 kts, it's the whole game.
Obviously the wider overall width and tail, bigger fin capability and rail design optimised for long reach/run course performance on the FW still delivers a significant difference; on the other perspective, the iS150 will be an "easier" and more responisive, reactive and potentially faster (Vmax) ride in these conditions - once you get it planing.
Cheers ~ Ian