Rman Level 1 backup

Hello All,

We have 12.1.0.1 database on Linux. DB size around 7TB. In the same server 2 DB's running. Both DB's started on daily INCR backup same time. Both DB's has BCT enabled , large_pool_size has same but PGA size is differ.

Problem here is ,

DB "A" INCR backup has been completed within 30 min (This is has more transaction on everyday)

But DB "B" has taken around 3 hr to complete ( This is less workload DB, as we can say simply running for any testing purpose) which has taken the Input size of the DB on around 3TB while backup running even though we have BCT enable. What is problem here, what are the things we need troubleshoot and change it for complete it sooner like DB "A"