40 watts charge faster. A 15-watt charger and a 40-watt charger, generally speaking, are 50 or 40 watts, and the charger is faster. Because the higher the charging power of the charger, the faster the charging speed, but this also depends on the device limit, in the support of the highest power of the device, the higher the power of the charger it uses, the faster its charging speed, which is in line with the basic laws of physics.