The 17 minute solution is as follows:
  1. A & B cross first (2 min)
  2. A leaves B on the far side in the dark and returns (1 min; total time: 3 min)
  3. C & D cross with the lantern (10 minutes for the pair, total time: 13 min)
  4. B returns with the lantern (2 more minutes, 15 total)
  5. Finally, A & B cross (2 more minutes; 17 total).

Of course, it took them 15 minutes to come up with this idea, by which time the zombies would have arrived. My brother-in-law suggested throwing the interviewer at the zombies and making a mad dash across the bridge...