Note, that some of these 15M are shared between processes due to Copy-on-write, if you preloading modules on startup amount of memory shared between processes will increase. Also I had good results with nginx + Starman.

PS: and there are some notes in the mod_perl documentation.

PPS: I saw in many places people run one apache with mod_perl and another one to serve static content and proxy dynamic requests to apache/mod_perl, but nowadays I don't think it makes much sense unless you're using specific mod_perl features, just use Starman instead of apache/mod_perl.