Please ignore the sceptics. Assuming that the car is well maintained, you can gain a lot of fuel economy. You can change your driving style; rest assured that you won't take 35 mins for a 15 minute journey.
-use the lowest viscocity oil written in the owner's manual.
-use the max sidewall (rated cold) tire pressure.
-avoid idling it to warm it up. Drive it off as soon as you turn the ignition key.
-don't exceed 2500 rpm, except when you are travelling above 85 km/h, in which case it can't be helped.
-shift to a high gear as soon as possible. People usually think ASAP means around 3 to 4k rpm. Its actually more like 2k to 2.5k.
-shut off the engine at red lights. There is absolutely no need to keep it on.
-conserve momentum. Don't race up to redline when you know full well that you have to stop at that red light, or there is a turn/intersection ahead. Also, maintain at least two car lengths distance at all times.
-drive at or below speed limits.
If it helps, I can achieve 15 kml from my ancient, oil burning, carb'ed Cultus in mixed driving. You have a much better car than mine, so you can achieve more.