Yeah just doesn't sound plausible to me. I've seen bigger projects take less than a minute on a 2014 desktop.

For big prod builds you'll definitely want to give the JVM at least 1gb of RAM, make sure you actually override Lein's defaults:

    :jvm-opts ^:replace ["-Xmx1g" "-server"]

Just as another data point, our project is 16k lines (including tests) and I just timed it at 2.7 minutes to run "lein cljsbuild once" with no difference when setting those jvm-opts. This is on a quad core 2.8ghz i7 MBP.

:compiler-stats has been a thing for a while now. This would give more information - like how much time in ClojureScript vs. advanced compilation. Also the compiler version matters - 1.7.170 is what you want to use. Otherwise you may need :recompile-dependents false.

Cool. I did not know about :compiler-stats. I'll check it out.