Here is the (unbelievable) reply from Audiusa:
"I am following up as promised in regard to your question about a trailer hitch for your 2015 Audi Q3. I contacted Andre in the Parts Department at YBH Audi. He confirmed that the trailer hitch is not an available accessory for your vehicle. The 2015 Audi Q3 is equipped with a 4-cylinder engine, and does not have enough power to support towing. As this is a safety concern, we cannot provide a recommendation on an aftermarket part that can be used.
While this is not the information you were looking for, I hope if provides some clarification. Should you have any additional questions, please do not hesitate to contact me directly at +1 877 615 2834 (extension 43215). If I am unavailable, please provide your reference number listed above and one of my colleagues will be able to assist you. We are available 24 hours a day, seven days a week to assist you.
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Come on! Not only is the hitch reciever needed for the bike rack accessory, it is available in the ROW for 4 cylinder Q3's. What a ridiculous answer! Oh, and the owners manual talks about towing...