john5959
Can I uninstall X3 now that I have Platinum?

NO!
Never uninstall a previous version. I have old projects that work fine in 8.5.3, but are a mess in X3e. Often it is the loss of paths used by plugs.
For most of the projects I have migrated to X3 I have had to clone all the tracks to get colors and icons to work properly. And had to create new buses to replace the ones that were silent without reason.
Sonar 2015 is NEW. It has issues. Just read all the headers of the many posts already identifying these issues.
Until you know all your projects will work, and that no bugs will interfere with how you work, keep the old stuff around.