Explanation:

✅ C. Divide the records in half and delete each resulting data extension
Marketing Cloud limits Contact Deletes to 500,000 records at a time, so deleting 1.5 million contacts requires splitting the data into batches—typically into three separate data extensions of 500,000 records each. Then you can delete them in sequence via the Contact Delete process from Contact Builder or API. This ensures performance and system constraints are respected.

❌ A. Query the records into a new sendable data extension and delete it
While querying into a new DE may help organize records, deleting a DE does not delete the contact records from the All Contacts table. You must use Contact Delete functionality (in Contact Builder or via API) to remove contacts from the system, not just from a DE.

❌ B. Navigate to Contact Builder and delete the data extension
Deleting the DE does not remove contacts from the system. Contacts remain in All Contacts even if their DEs are removed. To delete the actual contacts, you must use Contact Delete processes, which are different from DE deletion.

❌ D. Navigate to Email Studio and delete the data extension
As with option B, this only removes the container holding contact records, not the contact records themselves from All Contacts. Email Studio is not where you delete contacts in a compliant and system-recognized way.