Well that might be a little low, but not by much. 7-8 km/L would maybe be better, but in the type of conditions you describe 6 isnt that hard too imagine. If your milage was bad on the highway traveling 100kmh then you might have something to worry about, but city driving conditions are hard to typify since the can vary so much. So unless ure noticing other problems then I wouldnt worry about it. Hope this helps.
1985 190E 2.3-16
1957 220S(running one day, I hope!)