Have a look on the Audi approved website. There aren't many Q5's on there but when I looked maybe 3 months ago cars similar to yours were offered at close to list price. Admittedly thats just the asking price from a dealer and value will be a touch lower.
Additionally when i bought mine in Feb I got 9% off and it was delivered last week. In speaking to the same dealer she said that they would struggle to offer me 3% if I were to order again now. So in some sense that should have helped the value of your car. Agree also on seeing what a dealer will offer you but with some caution. Trade in they offered my ?23.5 on my RS4 which I declined, 4 months later I sold it privately for ?26.5k so that may give you an indication of the sort of margins they are looking at making.
Why not pop it on autotrader at list price and see what interest you get. It costs you ?40 and you are of course not obliged to sell it. Drop the price if no interest by 5% and then see what happens....
Good luck.