Excessive fuel consumption

   Dear members,
I recently acquired a 2015 model 308 SW HDI 181 horsepower vehicle at a distance of 154 thousand km. I noticed that the fuel consumption of this car is extremely high. I just use it to commute and go a long way. Of course I'm waiting for the engine to warm up. In other words, the vehicle goes 12.5 km with 1 liter. Factory features. He states that he can travel 25 km with 1 liter. This is a bit of an exaggeration, of course, but when they search the internet a little, those who use it say that this vehicle can travel 18 km with an average of 1 liter. The previous vehicle was a Jetta with the same tank volume and same engine size. I could travel 900 km on a long road with 1 tank. I'm barely getting 308 to 600. This is a sad difference and a little disappointed me. Technically, what do you think can be a problem in the vehicle?