Hi,
When I check on the destination volume, i see lot of snapshots which much older than the base snapshot still there and eating some space.
That's normal - base snapshot is your latest SnapVault update, so normally is pretty new, whilst all other snaps are your point in time copies, i.e. actual backups.
Can they be deleted?
Yes, providing you are happy with the fact these particular backups will no longer be available.
Regards,
Radek