I have an index which has 15 hosts and around 15 sourcetypes mapped to all hosts. How can I get events of only few selected hosts. (I cannot create separate index of those hosts)
You simply filter your search by providing additional conditions in your search. One such condition can be a list of possible values for a given field. Like
index=<myindex> host IN (host1, host2, host3, ...)
See https://docs.splunk.com/Documentation/Splunk/9.1.0/SearchTutorial/WelcometotheSearchTutorial