schema.execute is fast, but GraphQLView's get_response is very slow

* **What is the current behavior?**
I have a query that returns a semi-large amount of data (1.3MB, maybe 100,000 objects). When I run the query using `response = schema.execute(query)`, it takes less than a second to receive a response with all the data in response.data; however, if I query the data through the local Django server (via GraphQL Playground or my frontend application), it takes 10+ seconds for the server to send the response.

I initially assumed this was being caused by the serialization of the data from the database. I knew the queries were taking only 1/100th of a second based on the django_silk query/profiler results. However, the fast response from schema.execute rules out the serialization process being the issue.

Running cProfiler on Django doesn't appear to trace through the GraphQLView (any explanation of why this might be would be greatly appreciated). However, I was able to create a dynamic profiler with django_silk to confirm that it's something within `GraphQLView.get_response()` that's causing the slowdown

* **What is the expected behavior?**
I'd expect the response to not take 1000x as long to send as the time taken to query and serialize the data.

* **Please tell us about your environment:**

- Version:
```
graphene==2.1.8
graphene-django==2.10.1
graphene-django-optimizer==0.6.2
```

* **Other information** (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow)
[StackOverflow question initially opened regarding this matter](https://stackoverflow.com/questions/63964764/graphene-python-performance-issues-for-large-data-sets)