Doing so upgrades the site database and could render your site inoperable.
For more information, see Test the site database upgrade.
Configuration Manager does not support the backup of secondary sites nor the test upgrade of a secondary site database.
It is not supported to run a test database upgrade on the production site database.
They only apply if you plan to upgrade to the LTSB.
Later, when you run Configuration Manager Setup to do the upgrade, the prerequisite check will run again and evaluate your site based on the branch of System Center Configuration Manager you choose to install (Current Branch, or LTSB).
If you choose to upgrade to the Current Branch, the check for features that are not supported by the LTSB are not run.