How do you tell whether cutting your publishing volume actually worked?

I run content for a small B2B company and we put out about three posts a week. I've been assuming the volume is what's dragging the quality down, so I want to drop to one a week and spend the time on that one instead. I don't have much to base that on besides a hunch, and our traffic is already flat either way.

For the people who've made that switch, how long did it take before you knew whether it was the right call?