The instructions from Peter Wood helped. So I downloaded and installed Application Request Routing 3.0 myself.
Next I launched the FileMaker Server installer (14v2) and cancelled it after it decompressed. Than I changed the "Assisted Install.txt" file in the Files folder with installation files to have the license key and name already, so I don't need to enter it myself.
In the setup.ini I had to remove below the [ISSetupPrerequisites] section the first four lines for Application Request Routing. I installed this software myself before and FileMaker's installer fails to download it.
To run the installer, I run cmd to open a terminal window. There I use cd to go into the folder and run this command line:
setup.exe /V"/log FM14InstallLog.log ARRINSTALLED=1"
Please mind the quotes. The installer runs through like usual and I can setup my admin account.
Finally I have a FileMaker 14 Server running on Windows 10 with MBS Plugins and no problems so far