i remember in vanilla skyrim, you get one random world interaction every 5min or so. Is there a mod that reduce it to one random encounter per 2.5min? Or similar?

I don't think there is a mod or a command for it, but i found a mod that basically adds new encounters made by the author, not exactly what you are looking for but its worth a try.
http://skyrim.nexusmods.com/mods/29688