Answer
1,307,674,368,000
Work Step by Step
1st student: 15 choices.
2nd student: 14 choices.
3rd student: 13 choices...
...
...14th student: 2 choices.
15th student: 1 choice.
Using the Multiplication Rule of Counting (see page 298) with fatorial:
$15\times14\times13\times12\times11\times10\times9\times8\times7\times6\times5\times4\times3\times2\times1=15!=1,307,674,368,000$
