ArcSDE (10.2) Database connection is so slow on Oracle 11g

I create a enterprise geodatabase on oracle 11g by Enable Enterprise Geodatabase tool (From arcgis desctop 10.2). Everything works fine but connection is so slow. Only difference is , Oracle database is under IT dep control and other applications also using same database. There are so many users and tables. Their all tables are granted as public. So when i connected to database from Arc Catalog i can see the all that hundreds of table from all users. I don't know this can be reason of this slow problem. Because we test all network connection speeds are normal.
I have another oracle database with same specifications on a simple workstation (version 10.1), but database has only my sde users and tables. That one is so fast working.
Any one has some idea what is my problem?