I think the age of the bloke (I see you've assumed we're talking about a younger woman/girl and older man here but hey, let's go with it) does matter, because a 22 year old is much better equipped to coerce or manipulate a 15 year old into having sex than another 15 year old is, and also less likely to be interested in them because they are on an intellectual or emotional level, unlike the 15 and 16 year old or 15 and 15 year old are. Normal healthy 22 year olds don't tend to fancy people who are a good six years younger than themselves because the emotional maturity and intellectual difference will be fairly significant. Which means in most cases the attraction wouldn't happen in the first place. When it does, you have to ask yourself if it is genuine attraction, or if it's attraction based on the fact that the younger person is "innocent" and/or easily manipulated.
It's a totally different situation for 15 year old Mary to be in a relationship with John who is 15 and interested in exploring just like she is, who is as inexperienced as she is, who isn't expecting anything because they haven't done anything, to being in a relationship with 22 year old Bill who is super smooth, swans her around in his big fancy car, treats her "as an adult", plies her with gifts etc, except he's been with loads of women and she feels he has expectations. He promises her there is no pressure and only when she is ready, but she feels like he's being so nice to her and a man his age must be so experienced that he can't wait too long without sex. He makes little hints and tells her that she's okay and he will look after her, also hinting that he might get impatient if she takes too long. She convinces herself that it's no big deal and she loves him so it's okay and ends up having sex before she is ready.
That's not to say that Mike who is also 15 and a bit of a bully would be any less of a danger than Bill, but I think the situation with two kids under the age of consent is more likely to be a John one. Bill exists, most 22 year olds aren't interested in that kind of dynamic. Kids like Mary might "consent" but they don't know what they're getting into, not really.