I have a V10 Altitude but I think I can offer some advice, I think that the thing to remember with these cars is that their worst enemy is wind resistance and vehicle weight, I find that at 70mph with the cruise control switched on , I can see 30mpg indicated on the motorway as long as it's gradient free, however, go any faster or up hill and the mpg drops very quickly as the car tries to cut through the air, the other day I had the car remapped with a promised 2-3 mpg improvement, I am yet to test this properly.
I work shifts and rarely see a bad traffic jam as such, I see 25mpg on the 12 mile 30 min journey with good anticipation of other road users etc, one of the ways to get better mpg is to ease off the throttle when possible and let the cars considerable weight and inertia carry you, it makes a huge difference. Most drivers brake late and harshly, then have to accelerate again, using even more fuel...
Tyre pressures are crucial too, I checked mine (20"wheels) after I collecting my car from the dealer on my first day of ownership, the dealer said they had given car a 'once over' but the tyres were UNDER inflated by almost 20psi on the front!! and the screen washer bottle was empty...best to check them once per week. Such large tyres create awful drag at the wrong pressures, as will roof rails, air con..etc
Driving style will help too, also your area, lots of hills see the mpg plummet on my car, I think we can all agree that these Touaregs will never be the most economical cars, but we can do a lot to take the sting out of fuel costs.
I hope this message helps as I am a police advanced driver and my training helps me to get a decent fuel range with good observations and anticipation, it all helps and I'm sure that you will better these figures in the 2.5
Good Luck!