In general, when working with large datasets of data that remains relatively static, should caching be done on the WebAPI or Web Application side?

For example, we currently have a WebAPI endpoint that returns a large JSON payload. Usually this call takes anywhere from 30 to 50 seconds to return. We have been able to get around this by storing this payload on the Web Application but as more clients begin to consume this data it seems that caching on the WebAPI might be more beneficial?

What would you guys recommend?