As others have said above, you can keep your currently installed CS version and install CC from scratch without removing your existing software.
As far as the current project, personally I would recommend to hold off on migrating to CC until you finished all your current work. You can try migrating the project into CC, but that would most likely cause bugs and crushing, especially if your migrating from CS directly to CC2015 (that would be a three-software-versions jump).
You can always try to install CC and open the current project to see how it works, but keep in mind that after you have done some work in CC you won’t be able to re-open the project with older versions of CS.. So that might be risky if you start running into issues after doing major work on your project.