My machine isn’t that fast, but I can improve the boot time for the plasma desktop up to 25%.
How, it’s simple turn of ksplash.
8 sec plymouth (linux boot time) 11 sec ksplash 4 sec desktop is finished ===================== 23 sec (1/3 for linux 2/3 for plasma)
8 sec plymouth (linux boot time) 11 sec desktop is finished ===================== 19 sec (42% for linux 58% for plasma)
So with ksplash the computer need 15 sec to start plasma without it need 11 sec (-27 %) but the god thing is that it looks even faster cause I see plasma instantly after the login and as you can see in the lined movies the desktop flickering is also visible with ksplash. To be honest I like the deskop flickering, cause I see how plasma work.