Does any table hold data of all region 
1. if yes. Get a Materialized view created (replacing all_reg_view)

2. i see you already tried creating a staging table replacing the all_reg_view. 
Try creating cluster key along with partition.

Cluster key on the region (joining columns) and partition on some date column if available.

3. Analyze the other views for performance which you are joining with All_reg_view.