Please let us know the SR number once you raise it so that we may track it here in your thread as well. This way it also lets the Engineers know to come to the Community to see any/all troubleshooting that has occurred already so they don't duplicate efforts.
I do not believe that is possible in 7.1.5 simply by configuring prlogging.xml. The logs can roll daily, however, there is no way to set a limit to the number that are created. You could do this and then create a batch or script on your OS that can clean up old files in the log directory.
If I'm remembering correctly, the only way to control the number of log files created in 7.1.5 would be to roll the logs based on size. This will allow you to specify a "MaxBackupIndex".
This will roll logs based on size, generating log files PegaRULES.log, PegaRULES.log.1, PegaRULES.log.2, and so on. The log file with no number will contain the latest log entries, and as the number increases, the older the log entries will be. In the example above, the oldest entries will be in, "PegaRULES.log.10" once enough log files have been created to reach the 10th file.
The value of MaxFileSize can be changed to suit the requirement (100KB, 10MB, etc.). This will only create logs until the MaxBackupIndex value is reached. Once this is reached, the oldest entries will start to be lost.