The recommended service interval in the book is every 6000km.

Workshop here been living in the old kapzai era asking you to do unnecessary oil change every 1000km ~ 2000km. This is for bike with wet gearbox that uses the same lube for engine and gearbox.

Your scooter is dry gearbox.

However, by around 3000-4000km your engine will feel a bit heavy but does not mean the oil is bad. Changing oil around this mark will "lighten" up the engine.