Ok, so basicly I'm crying
I'm suffering from a cringyiest memory leak I've ever experienced in my life. I'm sorry for posting my issue at this forum, yet it's the best place I've found(
I tried to make my own modpack. This is the second one I do, and it's pretty much almost the same as a first one, which I've lost and currently trying to recreate (It did not suffered from my problem!) But now, when I start solo/multi game, in few minutes Minecraft RAM usage rises up from 6 GB to a freaking 12 GB, even through the limit is set on 7 GB. I have to say, that it's probably game internal code leak, because even if you pause the game (Esc), RAM usage still rises.
I tried resampling modpack for severing times, yet... it is what it is.
Yes, I know that it's selfish to waste your time on reading and answering this, like why even would you , but I'm in despair, sorry.