Table 3 tells you how long any subsequent dives can be—after your previous dive and before 12 hours have passed after your last dive.
Based on the information about the second dive, how long can the second dive be when considering the NDL limits? You know the new pressure group designation after 150 minutes on the surface is C, and you want to dive to 15 meters/49 feet. In Table 3, find the depth on the left. (Note: There is no entry for 15 meters/49 feet, so go to next greatest depth 18 meters/60 feet.) Run along the dark blue row until you are in column C. The maximum allowable dive time for the second dive is 33 minutes.
A PDC would most likely allow a longer dive time. Ask your instructor to help you with dive planning on your PDC if you have one.