There are 15 numbers, and we are choosing 5 digits.
__ __ __ __ __
Permutation means order matters, so there are 15 options for the first digit, 14 for the second, 13 for the third, etc.
15 14 13 12 11 = 15*14*13*12*11
But there are repeating digits in the set. We have to divide by the number of ways the 2s, 3s, 4s, and 5s can repeat. Since there are two repeating 2s, there are 2! different ways they can repeat. Since there are three repeating 3s there are 3! different ways they can repeat (using the same logic as when we did 15 options, 14 options, 13 options, etc.
(15*14*13*12*11) / (2!*3!*4!*5!)
However, this doesn't come out as an integer :( ... I'm not sure what I did wrong. Maybe you can find my mistake. Hopefully this helps anyways!