Unusual speedup observation

We had a discussion about a speedup when we built sysimage double times (replacing the older one).

Please see the discussion here: https://discourse.julialang.org/t/slow-julia-startup-time-after-sysimage-creation-and-an-unbelievable-observation/44102

It is a very big deal, because with this speed actually we can create many custom image and allow drastically faster development. If it found to be true with bigger names like this package organizer, then it should be noted in the julia's documentation for tips at workflow because this increase the adoption chance of the language with 10 fold, because it remove one of the main barrier for newbies.

Start by reading the linked Discourse discussion about startup speed after creating sysimages, then reproduce the reported speedup with PackageCompiler.jl and a larger package such as the package organizer mentioned there. Done means confirming whether the observation is reliable and, if so, identifying the Julia documentation workflow guidance that should describe it.

Written by the indexing model from the issue text.