This is on a 2012 MBA for a prod build. I see times of 140s or 180s on a fresh dev build. Times are lower on faster machines but still in the multiple-minute range. I'll tweak the build JVM settings tomorrow and see if that improves things.
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"]