Tesla's official marketing has a 10% to 80% charge at 40 minutes, and 10% to 100% at 75 minutes. https://www.teslamotors.com/supercharger
For a 90 kWh battery. I guess the Model 3 will have a smaller battery and less range, but practically speaking, filling up from empty is 5 minutes with Gasoline, and 75-minutes with the Supercharger (all the way to 100%)
You can get more efficient by filling up only to 80% charge over 40 minutes of charging... but that's still very far away from your claim of 15 minutes.