@The Aziz, I didn't want to go into specs and all that but I guess I have to. Not all specs but the ones that matter:
nVidia GTX 1060
Intel i7
16GB RAM
512GB SSD
Play all games at 1080p because of diminishing returns on performance vs visuals. This is all overkill just to play KSP, or at least it should be.
I duplicated issues without mods. Graphic mods make a huge difference, but the mods that have little impact are things like Mecjeb, Kerbal Engineer, and Kerbal Alarm Clock. I've been PC gaming and building computers since 95, troubleshooting others in 96(win95 MS Dos 6.2), and coding/scripting since 97. I'm not new to the nuances that effect game performance. I give credit where it is due and try hard not to be a fanboy. KSP is a great game, but it has some core issues that need to be addressed. You should be able to admit when there is a problem even if it's about something you really like. That's kinda the point of the original post and the video by @ShadowZone.