Customer wants to test the migration procedure from 14.5 to 15.0 but has no ability to replicate the production environment (due to a number of security, organizational and technical limitations).
Customer cannot use production environment for testing. On the other hand, the customer is not able to replicate the production in their testing environment and therefore perform proper testing there.
Version 15 provides new tool mogrify which is designed to facilitate migration between versions. One of the features of this tool is that it is read-only for the source environment (original installation). This feature allows the tool to be used in production with version 14.5 to read all the data and then to be used in testing environment to test migration to version 15. Since mogrify is read-only, it is safe to run it in production.