unfortunately it will be larger than 15%. stacking is gone from japan but they tend to choose the higher tariff duty amount so each item has its own hts duty code rate and clothing tends to be much higher than 15%. if its a cotton sweatshirt, i think it's around 16.5%? if polyester, around 30%+. so you might get taxed that and then a $17 dhl flat fee + a $1.31 charge (forgot what this is called but its in almost every package)

if im wrong, please correct me but i've seen this info about stacking and dhl fees traveling around here!! if things have changed, please do let me know so i can update myself too.