I wouldn’t invite either. The second has obviously been boosted, and the first is going to stand in stuff and die (because you can get away with that at 15 if you’re well geared, so it’s likely they’ve never learned not to do it). I don’t notice much difference between 15 and 17 now that I’m into 20s, but I remember how huge the difference felt when all I’d done were 15s and 16s.
(We do help other players out occasionally by accepting someone from the queue who isn’t really qualified for the key they’re queuing for, but we generally do it in a 15 to get someone a 15 for the vault, when we know we can easily carry them.)
Given the choice between inviting either of them, and not having the 5th, I’m pretty sure you’d invite the first nevertheless.
…or with 80 15s timed, they may end up not standing in some of the frontals at least. With that many runs, something will rub off on them.
I’ve met quite a few great players who I invited despite their score, for various reasons: I wanted someone who needed the dungeon timed for more than vault count, and I wanted to find people who didn’t have the chance to go higher keys yet.
I met someone in a +17, who barely had 2k score at the time, but a ton of +15 keys done. Next week, we took them to a +20, and they’ve been our best route planner since.
There are a lot of people out there, who are perfectly geared and capable of doing keys higher than 15, but for a whole lot of reasons, don’t really go there. They don’t get accepted to higher keys, because they don’t have any of those timed. They don’t run their own keys, because they hate assembling groups (hi, that’s me! whenever I run my own key, I’ll have someone else assemble the group for me). Or they’ve been spending time in raids or pvp and didn’t care until M+ until late into the season.
So, I’ll take that 80 timed 15s as a sign of experience, and I’ll easily take someone with only 15s timed (but many of them) over anyone who has a few 17-18s here and there, but considerably less keys done.
You’re talking about a situation that (literally) never comes up, so it’s irrelevant. And my answer is still the same. I wouldn’t invite either because I know someone better qualified would come along.