How are you deleting?
To Recycle Bin, bypassing the Bin, some other means?
(Recycle Bin has limited capacity [maximum size & probably inefficiencies when the number of directory entries grows too large?], I don't know specifics offhand, & could be purging itself in order to make room for more, only to have to purge itself ...)
Otherwise, IMO, it is often better to break a problem down into smaller parts. Like if you know a particular directory tree, a much smaller subset of your 450GB, with a smaller anticipated number of dups, would be easier to handle. Then pick another tree ... Get most of the crud removed in a more efficient way, then have a go with a wider birth.