Thanks for the early response received which was useful.I had query regarding the archive/purging,as I had done the activity but still I can see 15 incidents which are not getting archived/purged.Need assistance regarding it.
My two cents,
The only reason I can assume is those 15 tickets may have some parent ticket attached. Unless the parent ticket purged, the child tickets can't be.
Are they templates?
The ARCPUR.LOG and STDLOG would provide clues during the archive process as to why these tickets could not be archived.
Have a look at this KB article that may help to archive the individual\specific tickets:
Troubleshooting Archive and Purge, and specifying - CA Knowledge