The maximum number of rows that a DataTable can store is 16,777,216 rows. For the high amount of rows data the read range workbook take much time to read the Excel.
Instead of working with datatable you can select macros by vb.net. we have much activities in UiPath to use macros.
I have worked on 6 to 7 lakhs rows of data in datatable. But it was taking much time it was taking 1 and half hour. Instead of this I used macros it was completed in 15 minutes.