I'm actually relatively confident that you could get it down to 8-9 seconds to the basic X environment with an NVMe SSD and maybe even less if you were to cache some application states.
five seconds, year 2008: https://lwn.net/Articles/299483/
two seconds, year 2017: https://www.youtube.com/watch?v=IUUtZjd6UA4&t=17
The only differences between the system I used for benchmarking and my regular desktop was autologin, chromium in the startup script, and the enablement of the benchmarking thing. I'll probably poke around with it tonight and see if it's any different on my new laptop. This one had a proper NVMe as opposed to the m.2 SSD in my old laptop.
My Windows desktop at work takes forever to get running. Even after you log in and the desktop is visible it's another minute until it's usable.