What is a reasonable minimum time frame to retain queue, results, and completed schedules for in the Persistence Options in the Controller settings in a production environment?

For example, I have a customer with a setting of 90 days.
However, their MongoDB is quite large and causing some issues during upgrades.
Is 60 days a valid option here?
What considerations might I be missing when increasing or decreasing this value other than the amount of memory being used?