Are you using LDAP authentication or QC authentication?
You could use the Site Admin API to extract the data from the v10 system and then add it to the v11.5 system.
You could copy the Site Admin database from your v10 system to the system where you will install v11.5, and then when you install v11.5 you can execute an upgrade on the existing Site Admin database.
You could use the Site Admin API to extract the data from the v10 system and then add it to the v11.5 system.
You could copy the Site Admin database from your v10 system to the system where you will install v11.5, and then when you install v11.5 you can execute an upgrade on the existing Site Admin database.