What does “better sterilization” mean to you?
In terms of sterility assurance, and assuming this is moist heat sterilization, the process lethality (F0) can be used as a measurment of process effectiveness. More lethality gives better sterility assurance (SAL).
The first option: 124°C for 15 min, has more lethality (F0 = 29.2 min), than the second option (F0 = 5.9 min); so for sterility assurance, the first option can be considered “better sterilization” in terms of process lethality.