Banana Interface for SolR is slow

I have a search engine running with nifi dataflow and solr to index the data. I have used Banana as a user interface to query and display results, filter, sort and download them. All the instances - nifi, solr and files are in cloud.

Initially in my test phase when I had about a million files indexed, the interface was pretty fast. However, with increase in the number of files, Banana search is slow.

While the same query in Solr gives results quickly, Banana takes a lot of time. I was wondering if it is the number of files in the solr index that makes the search slow in Banana? What could be done to make it faster.