If I hold both personal and business Marriott cards, will I receive a 15-night credit toward status for each?
No. You will receive a maximum credit of 15 nights regardless of how many Marriott cards you hold.
This part form the Wiki is incorrect. My wife gets 30 nights a year by having a personal and biz Marriott CC. Her bonus nights hit late in the year, so I can't post a pic for now, unless someone can tell me how to get a detail of 2015's earned nights.