I think that 9 litre / 100 km is roughly 26 mpg, which does sound quite poor for a 2.0 diesel Leon. However, if you’re doing mainly town doing and (presumably) mainly short journeys, you‘re likely to be doing quite a lot of stop start driving in
lower gears and your car’s engine probably won’t be getting a chance to warm up fully, all of which will have a negative impact on your fuel economy. Also, lots of town driving probably means the DPF frequency is quite high, which will also have an adverse impact on your fuel economy. There will also be other factors that influence fuel economy - e.g.
- tyre pressures; if your tyres are under-inflated, this will have an adverse effect on fuel consumption.
- ambient temperature; with the diesels I’ve owned, I found that the fuel consumption was always worse in the colder (winter) months than during the warmer months.
- winter diesel; the change from summer to winter formulation for diesel fuel usually means fuel consumption suffers during the winter months.
- If your car is fitted with roof bars or a roof box, or you regularly carry other items carried on the car’s roof (e.g. cycles) that would create drag and result in an increase in fuel consumption.
I see from your forum signature details that you are in Italy, so it might be that in the region of Italy you live you don’t get particularly cold weather during the winter months. Also, Italy may not switch over to winter diesel, so the points above regarding winter temperatures/ winter diesel may not be relevant to you.
If you’re not currently under lockdown conditions that restrict the use of your car, it would be worth taking your car on a few longer journeys of, say, 50-60 kms or longer to see how your fuel consumption compares to your current long term average.