The answer is 113 ounces.
Kim's dog weighs 8 pounds. Since 1 pound is 16 ounces, Kim's dog weighs 8 × 16 ounces = 128 ounces.
As a puppy, Kim's dog weighs 15 ounces.
So, the weigh that Kim's dog gained is subtraction of 128 ounces and 15 ounces:
128 ounces - 15 ounces = 113 ounces.
Therefore, Kim's dog gained 113 ounces.