Time taken to execute query fluctuates

I have this query
GET _search

    {
      "query": {
        "bool": {
          "must" : 
                  [{"match" : {"track_id" : 4}}]
          
        }
      }
    }

However the time take fluctuates between 80 to even 300 or more.
e.g

{
"took" : 114,
"timed_out" : false,
"_shards" : {
"total" : 138,
"successful" : 138,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : 0,
"max_score" : null,
"hits" :
}
}

Have you tried using the profile API?

Which version of Elasticsearch are you using? What is the full output of the cluster stats API?