You are great! There is a type mentioned C15-2, which is not really compatible with the x152f, but I think its quiet simular. The control buttons and the position of the in/out connectors are slightly different. The monitor I have is produced in March 2000, so I think its too old to find a users manual in the download section of Fujitsu Siemens.
Anyway, thank you very much for your great assistance!
My best regards to you!