When the apps were updated new versions in new folders were installed. If you did not select keep older versions with you did the update then all of the icons you added to your tool bar would turn white and not work because you removed the older versions. You'll have to add new ones. This is normal in all operating systems.
I'm getting very quick ram previews in real time up to 59.94 fps in HD comps and 29.97 in 4K. You have your comp resolution set to Full and the Magnification factor set to 100% and I don't have any idea what size your comp is or how it is cropped in the Composition Panel. A better option would be to have the comp resolution to Auto.
I also don't have any idea what you have your preferences set to so I can't help you there.
This release does have a few bugs but a on every system that I have installed it on and worked with it's a vast improvement for previews and handling all of the footage types that I use in my projects. So far I'm fairly happy with this build and it has been my go to version for all of my work since the first half hour of testing. If I have a problem I have CC 14 and CC on my system so I can go back immediately to an earlier version of the software.
if you jump to a new version of any software or run an update without pre-planning for contingencies then loosing time and money is not the fault of the software. I always keep at least 2 previous versions of almost all apps that will allow multiple versions on my machines. I never do an update on software that will not allow multiple versions (like Adobe does) in the middle of a project, even if that project is going to last another couple of months without allowing a half a day for testing and reverting to previous versions. I keep a mirror of my boot drive at the last known working well for me state available so I can revert my system to a known working state in about 15 minutes. I keep all of my footage and my projects on a 3 drive hot swappable raid so I can loose two drives and not loose any files. I swap out one of the drives at least every week with one I keep in a safe so I always have a protected copy of my work. Those are good business practices that anyone relying on software to make their living should follow.