Do you have a toddler....how about something in that space for toy storage....a shelving unit with bins...a bookcase that you put the toys in and also bins for holding the small things. If you want something to eat on for two people, I feel it will be hard to find anything narrow enough and you have to take in consideration the heat register. If you have a pet rather than a toddler, then something narrow to keep his or her food, toys or leashes in.

Each diner needs a minimum of 24" wide, by 15" deep for comfortable dining. So are you looking for an eating surface 48" wide and 15" deep? You would eat facing the wall, and the chairs would stick out into the room. I don't know how you would get storage under it - where would your legs go?

One of my sons has a similar situation. He used a gate leg table that I had refinished years ago. A smaller table with both “gate”s down could be around that narrow. If you wanted extra table space the outside gate could be raised when in use. Coming up with storage underneath would be tricky but I don’t think impossible.

Ikea has a folding table with storage. Deeper than 15 inches though. Still, perhaps it can give you ideas on making something work for you.

Ikea - Norden

Look for a fold down table that attaches to a wall similar to a Murphy bed. Fold the tabletop down when needed. Place storage cubes underneath.