How to use Order Entry - Line Item BC

Hi,

We have Two Custom Join Fields in "Order Entry - Line Items" BC, due to these fields facing some performance issues while entering line items into an order.
(Join Tables are S_INVOICE and S_INVOICE_ITEM). Here we tried Database Advisory and created some indexes but not use ful.
To resolve this issue we have decided following:

We have Normal Sale order capturing and RMA (Return Material) Sale order Capturing.
Normal Order Sales Order:
In this we are trying to remove Join Fields (it means join is removed from Order Entry - Line Items BC and related Applets) which will used to improve the performance.