hm, is this new? I heard from this. Given I usually queued R15, I really didnt notice it got different, but I can remember two things how it was couple weeks ago:
a) when there is high population, u guys doing R13, never got into the same game as me doing R15s, and vice versa.
b) when pop in t5 got lower, i met oreg sometimes in a game, but mostly not, when he was using R13s, and me R15s, so it seems the queues get mixed sometimes.
c) when i equipped R13 purely, i usually got into destro games, where some use R15 ships, others T4, but if everyone used same ranks in the solo queue squad we usually ended up together.
d) i recently heard however, that others experienced getting thrown into r15 with pure r13 now, something that didnt happen back then to me, gotta check it out.
well, anyway, i think the only times we can draw definite conclusions is anyway, if we have many people to solo-queue at the same time, and i havent been in one of those occasions for a while. I can imagine they try to push you up by your rating.
Might make sense, might not, but anyway, take R15 and you ensure there is no bigger fish.