Repipe the main line?

The irrigation and the domestic water was connected to the same water meter in a commercial building (2" main domestic line with a T 2x1.5x2 to a 1.5 backflow for the irrigation). Two days ago the county installed a separate water meter 3/4" just for the irrigation. I had to cap the T and run about 6' from the new meter to the old line (backflow). I Checked for leaks and everything was ok. After running all zones, i noticed that the water meter is spinning slow. I checked it with my leak detector but I could not find anything. My question is: is it possible that there is not enough pressure (remember all valves are 1.5" and the connection is in 3/4) for the diaphram to close and the water is just running constantly slow? Do I have to reduce the main line and valves at least up to 1"?