Thank you all for your suggestions

1.5GB file every two hours and from multiple sources. Say there are n sources .. then n * 1.5GB files come into the file share.

The end users want to see...

No. there is no clustered index on the doc.CreatedDttm column. The createddttm field is datetime field and has the format of  'yyyy-mm-dd hh:mm:ss'

There is already a clustered index on BillingDocumentNbr...