15 km on 1 kg gas, is reasonable for a 10 year old car in City, as petrol per it wud be giving half the mileage, like 8 to 10, so i guess its fine, as long run mei apko 17-19 aram se degi. Get the radiator checked ASAP, or u mite stand sum where waiting for sumone to TOW it.
aur wesse bhe kharri garri Ziada kam nikalti, routine maintaince is beter, as Prevention is better then Cure