Can you describe *why *it is useful to wait 15 seconds before the service is restarted? That sounds wrong.

We have seen that spark master shut sdown when it has trouble talking to zookeeper, may be due to network related issues or if zookeeper is not functional. 15 seconds is just to provide some time for these problems to be resolved otherwise spark might be restarted but if there are still problems with zookeeper it might die again. This just prevents continuous restarts.