Its too low even in diesel, and if you are doing the same in petrol that means you are straining the engine too much which is not only harmful for the engine, but also killing FE.
You mean in diesel or petrol? Change the gear according to RPMs, not according to speed. In a good rev friendly turbo diesel engine like Hyundai CRDI or VW TDI, one should upshift after 2500 atleast so that you have sufficient RPM in the next gear. In the petrol, it should be around 3K atleast. Hyundai CRDI and VW TDI, both can rev freely upto 4500-5000, occasionally keep hitting that mark.
If you upshift at lower RPMs, than you are lugging the engine which finally results in low power and inferior overall FE. And there is turbo too (in case if its turbo diesel) which is also taking beatings and may die prematurely.
If you don't have road and just cruising, than can keep driving in higher gear but make sure that the engine is capable of keeping the momentum while you you have lightest possible foot pressure on A-Pedal, thats the key.