It will take 20 minutes to fill the cistern.
The solution to this question in 120 words:
The volume of the cistern is 1.5 m x 2 m x 1 m = 3 cubic meters.
The cistern is filling at a rate of 150 liters per minute.
1 cubic meter is equal to 1000 liters.
Therefore, the cistern is filling at a rate of 150 liters/minute / 1000 liters/cubic meter = 0.15 cubic meters/minute.
The time it will take to fill the cistern is 3 cubic meters / 0.15 cubic meters/minute = 20 minutes.
Therefore, it will take 20 minutes to fill the cistern.