When a virtual database (VDB) is being provisioned, Delphix first creates a virtual copy of the most recent datasource snapshot, and then performs a roll-forward recovery to the specified point-in-time using transaction logs. The more transaction logs (i.e. Oracle redo logs) that need to be applied, then the longer the VDB provision operation will take.
When the underlying datasource is a dSource, then snapshots are created by the SnapSync service, which uses the Oracle RMAN utility to capture changes in the source database. The Oracle RMAN utility is performing an incremental datafile backup to capture datafile changes, and unless Oracle Block Change Tracking (BCT) is enabled, RMAN must scan the entire database in order to find the changed data blocks within the database datafiles. If BCT is enabled, then the Oracle database maintains a separate containing a list of changed blocks, directly identifying which data blocks have been changed. This allows RMAN incremental backups to be completed very quickly. When an incremental backup is completed very quickly, then fewer transaction logs are generated during the incremental backup, and less roll-forward recovery is needed to provision a copy of the database to a consistent state.
In essence, faster incremental backups result in faster VDB provisioning. Please check whether Oracle BCT is enabled or not.