Someone released a mod called SloMod that drastically lowers population growth. I have to build farms just to make cities grow and usually it's at 1 to 2 percent even with level 3 or 4 farms.

I'm sorry I forget who made it but if you search for it you should find it. If you only want to have the growth changes and nothing else, just copy the descr_regions.txt file from the mod to your base campaign directory (backup the original). I think you will also have to delete the map.rwm file, not sure, but it won't hurt.