Renovating master bath on 2nd floor. Just ripped up a floor only to discover that the original shower drain is 1 1/2". House was built 1987.

Question: Can I proceed to install shower with 1 1/2" drain? I always thought showers required 2" drains. Thoughts?

Edit: Turns out OBC 1992 Table permits 1 1/2" drains for showers with only 1 head. Am I reading this right?