Could it be that this bow passive is bugged?
I've tried it multiple times but cannot see any difference in movement speed after dodging!? And 15% is not little; one would see a difference!
Could it be that this skill - for some reason - doesn't stack with the medium armor passive "Athletics"? (although that would only be while sprinting...)
Does this skill work for you? When I've got my bow skill at 50 I can invest a second point in it; 30% should be quite(!) significant (even for just 2 seconds; which is way too low anyway imo ).