This all started when I upgraded to Windows 10. Playing KSP at Windows 8 is butter-smooth. But now, I have to wait for like 30 seconds to wait until the start menu is responsive again. Same thing happens when I quit to main menu.
Already did:
Compatibility Mode (Windows 8, Windows 7)
Running the program as an administrator
Running the launcher as an administrator
Running in 32-Bit and 64-Bit modes
No, I'm not lacking at RAM.