Thank you very much for your question. Also thank you lematin for your reply.
I also agree to follow parts of the migration guide. Please note that every object, everything that you see in your device tree, is stored in PRTG's configuration file among other settings (e.g. Notification Templates, User Accounts, Web Server Settings, ...). If you want to migrate as little information as possible but the sensors and device tree structure is important to you, I would only copy the PRTG configuration file leaving the historic sensor data untouched.
Take the PRTG installer of the currently used version from your (source) PRTG Core Server:
C:\Program Files (x86)\PRTG Network Monitor\PRTG Installer Archive\PRTG Installer (Currently Installed Version).exe
Install the very same version on the new Core Server, stop the services on both servers and copy the PRTG Configuration.dat from the source to new Core Server. The file can be found under:
C:\ProgramData\Paessler\PRTG Network Monitor
This will copy the entire device tree and sensors among some other data, that might need to be removed afterwards to the new machine. Please also keep in mind that once you start monitoring from your new PRTG Core Server the monitoring requests to your targeted machines might come from another address which might need adjustments.