There are 651 permutations of 5 dice that sum up to 15 as follows:
They begin with these permutations:
11166 , 11256 , 11265 , 11346 , 11355 , 11364 , 11436 , 11445 , 11454 , 11463 , 11526 , 11535 , 11544 ........etc.
And end with these permutations:
63411 , 64113 , 64122 , 64131 , 64212 , 64221 , 64311 , 65112 , 65121 , 65211 , 66111 , Total = 651 ways for a sum of 15 on a roll of 5 dice.