Hi, you mean SAP R/3 4.6C ? That makes sense. But if you decided for a greeenfield, than you only get balance by year end and all open items e.g. open purchase order, sales orders. customer / vendor open items etc.
all the rest will remain in the old system which you need to freez for the periode of time required by your local auditors.
Taking over 15 years of data would be too much!
If you would like to do so than 4.6C Upgrade to ERP 6.0 EhP 7 and after that migrate to S/4HANA.
Regards
Thomas