RestRequest.Execute very slow on secured wifi

I am using TRESTRequest along with TRestClient And TRestRequest.

I have a URL that returns JSON. I have assigned this URL to TRestClient. I made the necessary connection between the above components.

Then I do RestRequest.Execute to get the JSON from URL. I am getting the result , buts its very slow. When I run the same URL on chrome its instant.

So further found out that its slow only on secured wifi. Response is instant on open wifi or mobile data.  

Please advice how can I fix this. Thanks.