Abdullah,
One thing you might consider is either disabling ARCHIVELOG mode in your existing VDBs (i.e. by going into SQL*Plus as SYSDBA, restarting VDB in mount mode, then ALTER DATABASE NOARCHIVELOG), or provisioning future VDBs with ARCHIVELOG mode disabled?
This would of course remove your ability to rewind that VDB between VDB snapshots, or prevision/refresh child VDBs between VDB snapshots, but you can compensate somewhat by taking more frequent VDB snapshots. The default VDB snapshot policy is daily at 3:30am local time, but you can alter that default policy or add a new VDB snapshot policy that would take VDB snapshots ever couple hours or every hour automatically. VDB snapshots do not consume much space, and certainly not as much space as archived redo log files do.
So, depending on your requirements, if you don't always need to arbitrary point-in-time recoveries, and if you have a really busy VDB on which there is heavy transaction volume, then you can lighten the workload on the Delphix virtualization engine, and also reduce space consumption by that VDB by running it in NOARCHIVELOG mode, and just increasing the frequency of VDB snapshots.
Please let me know if this makes sense?
Hope this helps!
-Tim