Correct Rutra.  I am in only PREVIEW MODE at this point.  I might have come onto something - not sure though.  I have one terrain in the back that is set to dynamic eco this takes forever & as I watch the bottom bar it says something to the affect of calculating the dynamics.  My other 3 terrains where populated the old fashion way - these render fast.

I've tested using render selected objects only.  The dynamic by itself(long time) & the other 3 terrains grouped by themselves & the render times are vastly different.

Looks like the dynamic calculations are consuming a good chunk of time & resources.

I'm just guessing at this point by it seems to be the culprit to date.  More research needs to be done here I do believe.