Signal 15 is sent to a process by the Linux
kill command. Is it possible that someone killed the process?
As per logs nobody kills it manually still looking for the reason...
This also occurred on the indexer level but instead with a signal 9 in splunkd.log for version 6.0.5, is this known issue?
There's a possibility that, instead of using splunk restart/stop/start, splunkd is used which is a daemon itself.