I have programs doing nontrivial things that run in 5 ms, from execve() to exit(). That's milliseconds, not seconds.

Exactly, even fairly complex script languages manages to boot, execute and exit in just a few milliseconds.

Maybe jigsaw is one piece in the puzzle to reduce the time it takes to start.

I doubt it's so bloody complicated, except AOT compilation of all system jars, I suspect it's mainly a matter of getting the time and resources to look at what happens when hello.world is executed.nu

That and relabling executable jars to jxe and the desktop is Java's to grab (that last part was a joke)