Bro, when you are neither using EV mode or ECO mode on, its called Normal mode. There is no button or light indication to it.
As for low average on only 3- 4 km drive on a busy traffic, you will always get 15 - 16 km/l average. Thats normal. If you happen to drive always on short intervals with heavy traffic, it is highly recommended to use Eco mode only then.
But if you drive over 10 kms or more daily, than normal mode would give you best mileage and drive pleasure