Comment by ToValueFunfetti

The most useful frame here is looking at log odds. Going from 15% -> 16% means

-log_2(.15/(1-.15)) -> -log_2(.16/1-.16))

=

2.5 -> 2.39

So saying 16% instead of 15% implies an additional tenth of a bit of evidence in favor (alternatively, 16/15 ~= 1.07 ~= 2^.1).

I don't know if I can weigh in on whether humans should drop a tenth of a bit of evidence to make their conclusion seem less confident. In software (eg. spam detector), dropping that much information to make the conclusion more presentable would probably be a mistake.