I feel the same way about my 2015 Street Glide... It's odd. I rented a 2014 Ultra for a day an loved it. It was the first time I rode the newer bikes. I like the street glide style and bought and immediatily felt what you describe. The dam thing just wants to dump over at low speed. It tracks ok and is not so bad up on speed, but at low speed it was complete crap.
First thing I did was pulled the forks and changed oil to Syn 10-30. added a spacer for tension and when I put together I set the forks 1/2 inch lower in the tree to get the nose of the bike down (bigger front wheel). I then chucked the rear "lowrider 11.5 inch" stock shocks and installed some 13 inch harley shocks from my 2002 (this is temporay while I shop for newer 13.5 inch shocks). I added a stabilizer to the rear mounts (still working on the front one). At this point the bike is probably 4X better than it was. The front end has stiffened up and not diving anymore. The lowered front and riasied rear has countered the effects of the larger front wheel and the geometry feels more right. I know my rear tire has a flat center... A new tire would make things much nicer too. When the rear is flat worn center on a wide tire it will also make the bike feel like it wants to fall over all of a sudden because you roll off the flat section and enter into the radius of the tire "which wants to rotate over" very quickly. Check your tire wear and be sure your do not have a flat middle. In short, start correcting evrything that needs to be corrected. It will resolve when enough things get fixed.
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