DS has moved into room 29 and is gradually asphyxiating the two remaining guards. I suggest someone follow behind and head right to deal with the two guards in that open C bit in room 33 and (eventually) the guy in the bottom right corner. Also, there's no doors between room 29 and room 15 - the guards there might visually confirm that the three guys in 29 aren't at their post anymore and raise an alarm.