To have best performance of your Rapid Planning functions, attend to Oracle recommendations.
Follow these implementation best practices to improve your performance.
Display only the columns in Supply/Demand window that you need to see.
Create a default Material Plan and view with Item/Organization/Week as filter.
Query a plan for only the items that you need to see. If you don't need simultaneous view of multiple items, query them one at a time.
When querying entities, use as many filters as you can.
Select only those rows to expand that you need, for example, to view pegging.
Export entities only when needed and export only the rows that you need to see. Do multiple small exports instead of one large export.
Do only one query at a time.
See Oracle Rapid Planning Installation Guide, Best Practices.