You mentioned that you've asked the Audi salon about the tyre size. I wouldn't take their word for it. Before jumping the gun and buying/using R19 rims, you may want to check your car's owner manual to confirm that you car can indeed handle R19 rims, and what tyre sizes are recommended for that rim size.
What's more, some countries (at least in Europe) have strict regulations regarding the allowed rim and tyre sizes for a particular vehicle. For instance, in Romania, each vehicle has a state-issued "Vehicle Identity Card", which contains a list of allowed rim and tyre sizes for that particular vehicle.
Using any rim/tyre combinations that are not on the allowed list can (and will!) get you in trouble during the state-mandated roadworthiness tests, and may even be illegal in some places!
Last but not least, as @Ben Thomas mentioned, there may be some insurance-related troubles, too. If you happen to get into a car accident and need to be reimbursed for the damages to your vehicle (assuming that the other driver is at fault, of course), the insurance company may check your vehicle's tyres. If they see that your tyre sizes are not on the approved list, they may refuse to pay for the damages, claiming that you are at fault for the accident because you weren't using approved tyres.