Yes, at those speeds, the fuel economy is extremely good. Those speeds are not practical on motorways may be (even though I think it will just be an issue of getting late to your destination), but on local highways it is a very practical speed and moving at faster speeds can be dangerous, since you never know when someone and their cow (literally, had this happen to me once) decide to get on the road when you are cruising above 100 kph.
On RPMs around 2k, the economy touches 20 kmpl. I have installed an OBD2 device and check the instantaneous economy often (The figures above are not from OBD2 port though, they are logs of fuel refill). The instantaneous economy is extremely good at speeds of 80-90, even better at 60-70, where it is ~20+ kmpl. But again, one does not want to drive on a mere 70 kph when one has to drive 400 kms.