Controll zwave switch takes long time by OH2

I do a couple times of experiment to control zwave switch device by SWITCH item on web GUI.

The time is really long in comparison to zwave protocol time, about 20ms.

Here is some record. (start time/end time)

Start time is I switch the SWTICH item on web GUI, end time is the
speaker connected to zwave switch turned ON off, almost the same as
zwave DEBUG log time. Most of the time is within in openhab instead of zwave binding.

Can some expert shed some light on how to shorten the time cost by openhab? Thank you.