Many boats go well to windward with just the genoa (and with the main furled). They balance very well this way, and go like blazes.
I've spent many, many years sailing in the Eastern Caribbean, and going upwind with just a genny is very comfortable. Lots of folks get it backwards: they furl the genny instead of the main. A boat with just main alone is a dog to windward...many act like you're "hove to" :-)
That said, a 150% genoa is a big baby, and you might need to furl it a bit in the heavier tradewinds. I used to carry a big drifter built of light nylon...about a 160-170% size....but blew it out so many times with 20 knots across the deck I finally had to trash it.
Try the genny alone first. Then, if need be, go for a smaller headsail. Or, possibly, think about recutting the 150% genny a bit. If it's a low cut deck sweeper, you could probably cut a considerable amount off the bottom to raise the clew, which would give you better visibility and more seakeeping ability when heeled. I did that 11 years ago with my No. 2 genny when I fitted a new ProFurl
furler, and that sail is still going strong. It sets pretty well when furled, too.....even WAY more than 10%.
Bill