VFD savings on Demand

Hi,
I am installing a VFD for a 15hp fan motor. It will definitely decrease power consumption, but my query is:

The motor is still same, so can we say that Demand KW is decreased?
If we decrease the speed by 20%, than can we say that motor is consuming 51.2% KW now?
If KW is decreased, then can we reduce the breaker size accordingly?

Thanks in advance.