Currently the binding updates the items whenever the controller pushes a frame onto the vbus. Beside what is necessary to program and use this binding I don’t know a lot about openhab, so I cannot say a lot about the mechanisms there. Anyhow I believe it is technically not the right thing to reduce the update rate in the binding (even though it COULD be done there). If you want to store data only every 5 minutes you should configure the persistence service accordingly. If you want rules to be evaluated only every 5 minutes do it there… What is your use case and why do you care to have “too many” update?
Edit: Note: there are no “requests” to the resol controller, the data is just pushed into openhab whenever the resol controller transmitted a frame with the data.