I’m also aiming for 10 days per level, and I’m just one level ahead of you. 10 days per level seems like a good pace for now at least!
Have you looked at the “Level 21 by 2021” thread here? We have a group that try to finish level 20 in 2020 and open level 21 before January 1st 2021. It might be a good fit for you!