What Does "15 Hours" Mean?
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I am always leery of first time RoadTrippers who specify the time of nearly thousand mile or longer) RoadTrips in hours. Such trips should be thought of in terms of days, not hours. Otherwise you run the risk of thinking that a "15 hour" drive can be done in one sitting or in one day. It can't. This is a two day drive. Make sure that you think of it in those terms and you can enjoy it. That's one of the biggest, recurring pieces of advise that we try, but often fail, to get across to people. Enjoying a RoadTrip take s time, time to drive safely, time to relax, time to not drive, but to get out of the car and actually experience something different. Otherwise, you might as well sit in your car in your driveway for 15 hours.
Now, all that said, there is plenty between "somewhere" in northern New Jersey and Atlanta. For starters, consider a couple of routes and sites along them down the east coast. More specific advice would require a bit more info on your interests, places you've already considered, and how much time you can devote to the journey. But if you are interested in wildlife not behind glass, consider stopping at some of the many National Wildlife Refuges along the coast, particularly on the Delmarva Peninsula.
AZBuck