Check Point recommends configuring Disk Space Management parameters to delete old log entries when available...

Check Point recommends configuring Disk Space Management parameters to delete old log entries when available disk space is less than or equal to a certain threshold. In this case, the correct threshold is specified as option D: 15%.

So, when the available disk space reaches or falls below 15%, old log entries should be deleted to free up space.

Options A, B, and C do not represent the recommended threshold for deleting old log entries according to Check Point's best practices.

References: Check Point Certified Security Expert (CCSE) R81 documentation and learning resources.