Regarding the sizes you mentioned 320 + 80 +75 +82 = 552GB - which is obviously more than 500GB - I assume you use thin provisioned virtual disk. In this case the additional disk space required to delete the snapshot could be anything between zero and the size of the snapshot, plus the disk space required for a helper snapshot, which will automatically be created if you delete the snapshot with the VM powered on.
Assuming the snapshot does not just contain additional data and the deltas - while deleting the snapshot - are not going to be large, it should be possible to delete the snapshot. I would however prefer to do this with the VM powered off to minimize the risk. Please keep in mind that deleting a 75GB snapshot might take a few hours.
Ensure you disable VDP while you delete the snasphot, to ensure it does not try to create a new one during this time.
André
