Backup of DCBF time has increased by 15 to 20 minutes

We are using Dataprotector A.06.11 on Windows server 2003.  Within the last two weeks our daily backup for the internal database has taken an extra 15 to 20 minutes to complete. (the total amount of data we are backing up has increased over the last year)  On the server, DataProtector is installed on the C drive. However we have the DCBF folder on the I drive titled DCBF3 with a path of I:\dataprotector\DC\dcbf3  (we did this several years ago due to space concerns), The DB40 directory is on the C drive as normal under Omniback directory (there is no dcbf folder in the DB40 directory).  I monthly perform an omnidbutil -purge -filenames -force which doesn't seem to help. I tried the omnidbutil -dcbf but I don't believe it is working on dcbf3, it reports Done in a split second. How do I improve this backup time and decrease it? Is there a way to purge dcbf3 which is on another drive then dataprotector is installed?