I would also find another trainer. Your dog is deemed aggressive at 15 weeks?? The dog park is the worst place to take a dog that is in your dog's condition. Other dogs will sense the fear and it can turn into something ugly quick. My puppy was attacked at the dog park....I never brought him back. But I did keep taking him to his puppy classes, on controlled walks to the park, and even to the pet store. 2.5 years later my dog is fine. You have to keep moving forward or the dog will not get over it.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD