Alright, there’s not much more we can say about that without further info. The binding is capable of hitting TCP faster than that,but something else in the system may be throttling it.
You’ve seen the “performance management” post. Such things are always a balancing act amongst stuff that is important to you and stuff maybe less so, but subdividing brings its own overheads, etc. etc.
Set up your best guess at one device, and lets see what debug info you get.
Yes, if you can get a karaf console up.
Hmm. Even at best, in this sort of usage you might end up with a half-second delay getting an event to openHAB over Modbus. That’s noticeable at human scale. Then if it’s supposed to “do something” via rules there will be further delay.
I have an on/off lighting switching system myself, linked to openHAB via Modbus. But made the deliberate design decision that wallswitches clonk relays directly; fast response.
openHAB is added on top, listening in to events and able to exert auto controls e.g. motion activated, but not in the manual control path. Seconds delay matters little.