Solr delay in writing response (delta between qtime and real time, delay in response chunks)

Question

I have started facing issues after upgrading to solr version 6 from solr 4. The response time of queries with larger response > 20KB has increased significantly. Upon looking at the response i see there is huge difference between qtime reported by solr , first byte and the last byte. Qtime:- 10ms , first byte :- 60ms and last byte 250ms. Looking at the tcpdump i see there is gap of almost 20 to 60ms between response chunks sent by solr. This happens with just executing single query as well.

Further information

My question is specific to if somebody else has also had the same behaviour with solr6 and what could be causing this issue and how could i mitigate this. Does not seems to be tomcat solr6 is hosted on, also i am running on host with 16GB memory and there is plenty of free memory left. CPU is also not saturated. To me it seems like its coming from solr response writer method. We are using tomcat instead of jetty as it comes in bundled with DSE package which we are using as our database backend for solr. I have checked from database side and its fine. It just seems to be issue with getting stored field and writing/streaming response from solr side.

Further Information

I have not yet contacted DSE support yet and using javabin for response writing.