Is there any issues doing this?
At least keep a backup of the iPhoto Library on an external drive.
We have seen several cases, where suddenly a problem turned up in the Photos library that only could be fixed by repairing the original iPhoto Librar i iPhoto and repeating the migration., for example, if the connection between the edited versions and the original image files had been out for some photos. Such problems can go undetected for a long time, and you will only notice them, when you try to edit or export the photos. So keep the original iPhoto Library until you are reasonably sure, that all photos migrated well.