Quick blow fuses have a defined ceiling where they open, in this case 150 amps is the max, 151 amps will open the circuit. A Slow blow fuse or circuit breaker opens with an inverse time delay. In other words it will allow "overcurrent for a time" The higher the current the less time before it opens. It is not unusual for a motor to use 300% of normal full load current for a short time when it starts. This amount of current would overheat the wiring if it continued but is fine for short period. I'll bet the 120 amp fuse would be fine at 300 amps for a few cycles (hertz) A good use for quick blow is sensitive electronics where any overcurrent is a sign of trouble.
Tom-retired (My last day as a professional electrician was last Thursday)