I've decided to try switching my rapid from 10 min to 30 min, as I keep missing threats and I also need to regain the elo I tilted. However, I know that matchmaking for 15/10 and 30 min starts to become hard at higher level, so my question is, at what rating does playing 30/0 and 15/10 become hard? I know I am probably quite far off, however it could become a problem if I do.
Around 1900 for 15|10, I don't know for 30|0, but it was really hard to find opponents at 1800 for 30|0. If you hit one of these barriers, consider going to Lichess, here you can even find opponents in under a minute for 30+20 time control! I play slow chess there.