19.2
To find the hypotenuse the equation would be: a^2 + b^2 = c^2.
12 squared is 144 and 15 squared is 225. Add them and you get 369. Then, square root 369 to isolate c. It'd be about 19.2
Because they are using flat nets they may be able to get more boxes per area of cardboard purchased instead of purchasing the boxes and losing some extra cardboard from a cutting or gluing process. the flat nets may also be cheaper to ship or take less area than boxes shipped whole.
Answer:
due to not much information given and the way you ask the question I would definitely say no
