150 in-lbs is 12.5 ft-lbs.
Not that the proper torque isn't important, but even more so than the actual proper ft-lbs or in-lbs (whichever it may be), is toquing them in the criss cross pattern and torquing them evenly. If they're not torqued evenly, you'll have issues. If the numbers are off a tad, but they're all even, you'll be good.
If you don't have a torque wrench and can't afford one, you can rent them from auto zone and places like that. I'd save up for one though. They definitely come in handy!!