The U consumed for 15 minutes and 16 minutes should differ by a factor of two. The U consumed in one month for 15 minutes is 50, while for 16 minutes it is 100. In one month, the amount earned from 16 minutes compared to 15 minutes can earn one more token, but currently, the chance of earning one token that can be sold for more than 50 U is relatively low; most are sold for less than 50 U. Therefore, whether to do 15 or 16 times a day depends on yourself.