Hello Bill,
Personally, I would exercise extreme caution with this. After all, what you are considering is to is to depart (albeit slightly) from the manufacturer's recommendation simply to save some money. Audi would have developed this car and decided what was the best tyre size for its power and handling characteristics. The final recommendation would be to consult the car's handbook and see if the undersize is indeed a recognised alternative to the ones on there. If so, great. Of not....?
I guess it's not out of the question that a previous owner may have fitted an oversize! - the handbook could be the best source for you, and always worth a look.
Of course the final decision will be yours, but if you did find yourself in a claim situation with your insurers at any time, then they might just look upon this downsize unfavourably. If it were mine, and you decide to go for the cheaper option, then I would at least pass this passed your insurer just to be sure.
Not sure if this helps or hinders, but I think you are very wise to seek advice.
Good luck with whatever you decide to do.
Kind regards,
Gareth.