always check fuel average by filling the tank to full again, by exact same method you did the first time. For example, if before test you got the tank full by petrol nozzle automatic stop then fill it again by the same auto stop method.
at 60-80 km speed in city, i think average is okay. but for highway, it is not enough.
you have to choose one method, city vs. highway drive, so you can get a clear picture of fuel consumption...
because in this situation, out of 300 km run - you did 80 km on highway and 220 km in city drive, and 15.6 km/l is good average in that aspect.