To fill dead space, consult a taxidermist or a lighting specialist.

LOL!

Kay, it depends on the space. I dislike the look of start and stop cabinets, though it works in some designs, especially with wrapped moldings or wide windows. Mine is about four feet. Aprons--panels that hide the lights--are out, but I wanted something, so I had a bridge cabinet made. It houses the lights for the sink and the heat register, which couldn't be moved away from the wall. Instead, there's a flexible duct with a grill on the front of the cabinet.

This is a mid-construction picture where you can see how it works. Over in the hole for the fridge is the door (which lifts), with the hole for the heat register grill.

If you wanted to do a bridge, you'd end it at the same height as your other cabinets, unless there were a good reason to go to the ceiling, like the heater duct. :) If your 15" cabinets are 15" high you can carry them across. If you meant 15" wide, yes, you could repeat the glass (go frosted to hide the light cans), and repeat the bottom treatment (light rail or whatever) that you have in your other cabinets.

You could also do a high shelf or two, either cabinet wood or glass or wire. Or you could do a version of a doweling plate drying rack.

Another way to handle it would be to curve the flanking cabinets if those are 15" wide, to soften the transition between the flank of the cabinet and the depth of the wall. Or do an homage to the '40's and have little curved shelves on either side. Or put in a really cook piece of art over the sink (so long as it doesn't block the lighting). Or hang a trio of pendant lights.

A lot of what to do depends on what the whole room looks like...