Not really, a flat +3 means that 45% are 15 or more (and 50% are 14 or more). I wouldn't call a relative 6% difference "pretty big".
With +3, 15% are greater than 20, whereas with (roll two), 0% are greater than 20.
With +3, 0% are 3 or less, with (roll two), 2.25% are 3 or less.