Significance of the 15% tariff number

Taiwan has made an agreement with the US that will see US importers paying a 15% tariff on Taiwanese products. The 15% number might have additional significance—if the US Supreme Court rules some tariffs illegal, one alternative route is for President Trump to impose a universal 15% tariff. Taiwan pledged to increase investment in the US—some of this will be already planned investment, and markets have learned not to take such announcements as definitive.