You don't have to invest -all- your 150k that is on the sidelines tomorrow. What you can do, is add it in over the course of 1-2 years.
Can a market crash happen after all your money is in? Yes. But over the long run, you'll come out ahead investing your money over -not- investing it.
I'd read Stocks for the Long Run, because it has passages in it about time to recovery during previous market crashes, one of the standout lines of which that has stuck in my head, is that during the 1929 crash, if you had invested your money the night before, you'd be back in the black on an inflation adjusted basis after 15 years. On the one hand, 15 years is a long time, but on the other, after that you start coming out seriously ahead, and if you never invest, then you never reap the rewards.