I had a plumber swap out the sinks in the photos below. Sinks are in the same bathroom and appear to be on the same drain lines. But with drywall that's not 100% certain. Anyway, the sink on the right  drains slow and an occasional air bubble comes up. Sink on the left  works fine. Could this flow difference simply be because of the drain discharge height? Left sink has an additional extender vs right meaning the water is flowing 3-4 inches lower vs right hand sink. Does water velocity matter? Is this a ventilation issue? Would a 2" drain be better? Should I pipe the right sink over to the left with a 2" line? Any idea on how to fix the problem????