Assuming the boat is not running, 1.5 to 2 hours is just about right. For some reason we see this with the JL 1000/1 as well, JL mono blocks are power hungry for sure, they suck it right out of the supply.
You are running 2700 watts, so estimated amp draw of about 270 amps (estimated) your batteries contain 220 Ah, so 1 hour at max volume, ~2hrs at "half" volume. These are rough numbers not exact calculations, but you are not all that far off.
I have 4 2400s and 3800 watts and see about 3 to 4 hours if I run the boat and get my alternator on the higher end of it's output every hours or so to allow the amps to cool and recover for a heavy duty cycle.