This mod allow multiple configurations of the file randomevents.meta, that allow the time that takes trigger random events and the frequency that this happens while in free roaming.

Replace in your game folder in the file x64a.rpf/data/tune/randomevents.ymt.

YMT Files: http://gtaforums.com/topic/798577-how-to-edit-most-ymt-files-right-now/