Thill .... I mostly catch Warmouth & Green Sunfish "if" I get my jig too close to the shoreline (<2fow). Crappie are usually suspended in the darkest shade under a dock (or pontoon parked under/by the dock & in the water) ... sometimes high in the water column & sometimes close to the bottom, but usually around one of the posts (if it's a stationary dock) or around brush/trees that are under the dock or hanging from it. I generally shoot the dock from several different angles, first ... and try and cover as much of the water column as conditions allow, then finish fishing the dock by Vertical Casting the outer, deep water posts. Vertical Casting also works very well on bridge pillars. Here's my article on "Vertical Casting" - Crappie Pappy Article

I don't slow troll jigs, I Push them .... and if I need to get the jig down to the 15-20ft depths, I'll use whatever amount of weight it takes to keep my lines at a 45deg angle at whatever speed I need to go. That may be 1/2oz or as much as 1.5oz of weight & my speed may be 0.5mph to over 1mph. I do that because I know how deep my jig is by multiplying the length of line I have out (below the surface) by 0.6 "IF" my line is at a 45deg angle. So, if I have 20ft of line below the surface & the line is at a 45deg angle, the jig is about 12ft deep (20x0.6=12). If I needed the jig to be in the 15-20ft depths, I'd let out 25-30ft of line below the surface to get to 15-18ft deep (25x0.6=15) (30x0.6=18)