I had the same problem with this version.
I have overpass this Freeze/Slow Issue by deleting "jre.bundle" file inside the SoapUI application package content (optio: "Show package content"). You can find this file under the directory "Contents/PlugIns".
After I doing that all issues regarding Freeze/Slow disappeared.
I believe that the problem might be with this particular Java engine that comes bundle with SoapUI. When deleted it uses the default installed in your OSX, usually the last Oracle Java machine.
Hope it helped.
