Hi,
There have been a number of users who have upgraded to 4.6.1 and versions after that and have not reported performance decreases. A ten times performance decrease sounds pretty significant. I definitely have not noticed any slowdown in the startup page. This may be a connection or service difference on your side.
What can help diagnose the problem would be to profile SoapUI for the slower versions versus the faster versions. Using jvisualvm.exe that comes with the JAVA 1.7 jdk can help to do this. Copy the results done and post them here.
https://visualvm.java.net/profiler.html
