SoapUI 5.3.0 and external JAVA 8

We are currently running SoapUI Open Source 5.3.0 (Build 20161130-0556) on Windows 7 clients using the included JAVA Version 1.7.0.55, which is running well.

While developing a client package for Windows 10 we are removing the included JAVA Version from the package (removing the JRE folder). Thus the already installed JAVA 8 version shall be used (SE 1.8.0.172) for running SoapUI.

When starting SoapUI as a normal user it hangs at the splash screen until Java is killed from the Task Manager.

A workaround to start SoapUI as a user with local administrator rights (NOT "run as Administrator") works, but is not applicable as a solution.

Any ideas, how to get it running also as user with normal user rights?