Welcome to the forum!
Towing with these things can provide a variety of consumption figures depending on the terrain, the traffic and your style. Pushing it over 2500rpm is going to make it drink fuel like a lonely guy in a bar full of ugly chicks.
We've had ours down to 15.5LPHK and up at almost 25LPHK while towing. Hitting the accelerator hard isn't going to help and constantly stopping and starting (traffic) is a pain in the tail. Gently bringing the vehicle up to speed and avoiding hilly areas is about the only way to lower its consumption.
Anything over your engine's peak torque curve is going to be wasting some fuel too. Torque rises in the 4cyl diesel from about 1500rpm to a peak at around 1800-2000rpm which equates to around 95km/h on the road. Trying to go any faster will end up using more fuel for less gain - because you're beyond the peak efficiency spot of the motor.
Hope that helps.
