For my next campaign I won't be touching the building times, but I've reduced unit recruitment times by 1 turn in the export_descr_unit file. Most now have a recruitment time of 0, with elite units on 1. This prevents Praetorians, Pharoah's Bowmen etc. being cranked out by the bucketload, but allows armies and fleets to be built up quickly. It's also handy if you want to migrate large numbers of peasants from the centre of your empire to the underpopulated fringes.