We can’t transfer the wiki data from the old (15.10) to the new xwiki (16.2) which is on a new server with updated Java.
The export-Import application does not work and exporting with the filter-stream application works neither.
Problem definition
Securing the wiki with: Administer Wiki => Content => Export as XAR-File. Version of the wiki 15.10
Importing this file via Filter Streams Converter into an XWiki 16.2.0.
Either update the old installation to the new installation version, then export-import (or maybe migrate db and data?) or install the old version in the new install, export-import (or migrate), then update the new install to the new version.
IIRC it has never been suggested to export-import between different versions, but wait for other answers too.
Yes, this is not the recommended way to upgrade XWiki as you loose a lot of information. The recommended way is to use the regular upgrade procedure. This is also mentioned in the upgrade guide at https://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Upgrade. Upgrading to a new Java version is fully supported with a regular upgrade. Just make sure you move all data to the new server.