150cc carburettor bikes with similar performance but better electronics (economy mode selection) can easily go around 60 km/l.
Many of the Chinese 150cc bikes are designed for economy and go upto 65 km/l or more, but the top speed of those bikes is around 100/105 km/h. You have to ride them at 65-70 km/h for best consumption.
One has to ride easy, just below or around the max power/max torque RPM, avoid braking by slowing down early, and no sudden acceleration. At 6,000 RPM, GS150 has a speed of ~72 km/h and at 6,500 RPM, ~78 km/h. So around 75 km/h it gives the best consumption. Also, Lahore to Abbottabad is 400 kms, except for Lahore-Gujranwala, the road is mostly good and at this distance the economy is generally better.
You have to choose between speed and economy, with the bikes available in Pakistan, you cannot have both. With EFI bikes you can have both.