Improve performance while Traversing List
You can actually change the performance to O(n) by changing one line of code here (and adding a couple of imports):

import java.util.Set;
import java.util.HashSet;

...

private Set&lt;String&gt; listTempName = new HashSet&lt;&gt;();


Although this works, we can simplify the code a little bit. Effectively, you want to see if the list of elements in the given List are unique. There's a really easy way to do this: add them all to a Set. If the size of the set and the size of the list are equal, then there are no duplicates. If the sizes are different, then there must be 1 or more duplicate elements. With this, we can simplify your code to:

public boolean isPreviousNameExist() 
{
    for(String name : listNames) {
        listTempName.add(name);
    }
    return listNames.size() != listTempName.size();
}


A slight improvement based on comment by @bowmore:

public boolean isPreviousNameExist()
{
    for(String name : listNames) {
        if(!listTempName.add(name)) {
            return true;
        }
     }
     return false;
}