Backup Server versions 15.0 ESD #2 and later generate a different format of compressed dump than earlier versions.
Therefore:
You can load compressed dump made using a Backup Server version 15.0 ESD #2 and later only into a pre-15.0 ESD #2 installation using a Backup Server version 15.0 ESD #2 or later.
If you are using a pre-15.0 ESD #2 installation and want to use your dumps for an archive database, use Backup Server version 15.0 ESD #2 or later to create compressed database dumps.