Answer: 1/210
Step-by-step explanation:
The positions of Drea and Bryan are locked in as last, and 2nd to last respectively. This means the 15 slots drops to 15-2 = 13 slots.
There are 13 other people and 13 slots to fill.
That gives 13*12*11*10*9*8*7*6*5*4*3*2*1 = 6,227,020,800 different permutations where Drea is last and Bryan is 2nd to last. Order matters in a permutation.
This is out of 15*14*13*12*11*10*9*8*7*6*5*4*3*2*1 = 1,307,674,368,000 different ways to arrange the 15 people. This larger count will have Drea and Bryan move to other slots.
If you divide the smaller number over the larger, then the block "13*12*11*10*9*8*7*6*5*4*3*2*1" cancels out.
We'll be left with 1/(15*14) = 1/210 as the final answer