Cat api calls take long time to respond

I have a elasticsearch 1.5.2 cluster which is working fine. Sometimes when I query its cat apt, for example "curl 10.1.1.1:9200/_cat/nodes" it takes long time to respond. For that reason, KOPF and Kibana also takes long time to display data.This happens randomly. I have enough resources allocated to the cluster and could not find any errors in the logs. Has anyone experienced this issue or has a solution ?