With jigs maybe?
LedHed said:
.......how would you fish this damn - I mean dam - area for crappie?......

Just kidding, sorta. :jig: I would be using jigs.
Almost every one of my small local lakes that hold crappie are upground reservoirs that have nothing but a rip-rap shoreline the entire way around and have a fairly steep drop. They are totally devoid of cover. Water clarity is usually very good, anywhere from 4'-6' of clarity all the way up to crystal clear with easily 20'+ visibility. One lake in particular, have seen bluegill and crappie both spawn out in water over 10' deep!
How is the water clarity? If it is pretty clear, chances are they won't budge from their comfort depth until low light conditions. Twilight hours are best for me when the water is very clear. Holds true for both crappie and walleye. They start rising up in the water column as the sun goes down and are a LOT more willing to bite.
Are there ANY weedy areas? If you can find weeds in that 15' target depth... maybe you could find some more concentrated schools. If not weeds, look for any structure or changes in uniformity at the depth you are showing suspended marks. Just may find a few that are feeding in the 'diversity zone' and a little more willing to bite.
If jigs don't do it alone, set some slipbobbers at your target depth you are seeing marks... hook a minnow through the nose onto an 1/8th oz jigs..... start dragging it around.