Hi, the total weight that a Boston terrier cam reach is 25 pounds, so, that weight must be equal to the actual weight of a puppy of that breed (15) plus the remaining pounds to reach full weight (w)
Mathematically speaking:
15 + w = 25
Solving for w:
w =25-15
w = 10 pounds
This dog could weigh 10 pounds more.
Feel free to ask for more if needed or if you did not understand something.