Excel is never really a trustworthy and good as a source, as too many people enter data differently in Excel which usually creates headaches over headaches in dataloads. Excel keeps a static version of data, the only thing that is living is a growing number of versions on various notebooks and you are never certain if you got the latest and most recent version. Excel just can't take 2 million records.
If you have to deal with that many records then you should have better tools than Excel as medium between a source and a target system.