I was stuck at an average of 22-24 for several monthsNow I've switched method, and I'm almost back to this speed again... hopefully I can actually improve consistently rather than randomly. But I'd definitely say sub-20 was the hardest barrier for me, just because that was when I got to the time when repeatedly solving didn't help. And it still doesn't.
yes it helps alot, but i think what happens is that you dont improve as fast as you used to and really feel it. i was also stuck at like 27, then lower 20s and i also didnt feel improvements for kinda long times, but i kept on solving without really worrying about my speed just trying to do f2l better, it felt like doing the same pointless thing over and over but its so important to just keep practicing, especially when you feel like you are stuck cause thats when you really need to practice. all i can is say is that its totally worth it and i am like always sub 19 now, on good days even sub 17 and sometimes sub 16 and im at a point again where i can see myself getting faster and faster, especially since i havent even learned full oll. hope that motivates you