what is the probability of getting all questions right on a 15 question, 3 multiple choice (each) with just guessing?

Question

i did 15 C 3 and got 1/455

Answer 1

or is it (1/3)^15??

Answer 2

prob(right) = 1/3

prob(all 15 correct)
= C(15,15) (1/3)^15 (2/3)^0
= 1/3)^15