Who knows? Why do you think only people who have gotten to $15K MRR can offer value?
I agree it's something of a signal, but I'd personally consider that a very weak signal. shrug
In that case, we fundamentally disagree, and this discussion is fruitless.
There's also the problem that you don't know the value of the hypothetical "person who hasn't gotten to $15K MRR" yet. If they started their company 2 weeks ago, they probably have an MRR of $0. Does that mean that they have nothing of value to tell you? That depends on a lot of other variables.
Anyway, you're probably right... we probably just have fundamentally differing world-views. I lean towards the "you can learn something for everybody" mindset, and try to late-bind judgment on people's value as advisers until the last possible moment.
It's a pretty good barometer for success - 99% of founders don't get to that point.