Waited 15 mins for a shack burger only. Couldn't ...

Waited 15 mins for a shack burger only. Couldn't wait any longer - at the rate the servers were going, it looked like it would be at least another 10. Not sure what was happening in kitchen, but no one was being served! Had to walk away to catch my train. Order was placed at 11:50. Walked at 12:05.