I have used Belta 2007 for about 5 years, last year gave it to a friend... My average for those 5 years was around 15....
Don't push the car too hard i.e. let it itself pickup the speed don't race.., and always maintain a speed 90 ~ 105 on motorways,
Clean/ change the plugs, get the throttle body cleaned and check if the cat converter is still there, it must have been already removed.
Also check air pressure in tires regularly, keep it at 30