More like 3.75% to 6.6% at most, depending on the bean. But this is not a very good way to think about decaffeination because coffee has to be below 0.1% caffeine by dry weight, regardless of bean, to qualify as decaf, pretty much as a global standard.

A mug of decaf has about 3% of the caffeine of a mug of non-decaf coffee, at most. It is negligible as a stimulant. The only people who would need to avoid it are those with an allergy.