Hi Samid
Check in ST06 the memory (swap) and CPU usage.
In fact the average response time for Dialog & Update process are not great, with quite an high ratio of DB time.
Make sure that the Oracle statistics are up to date, make sure you have run the script from note 1020260 - Delivery of Oracle statistics (Oracle >= 10g)
You can also check these generic notes
1918774 - Performance issues when running an SAP Installation
618868 - FAQ: Oracle performance
Best regards