There are a few basic calls for Insight, l list some below, but there are several more..
https://developer.cisco.com/meraki/api-v1/get-organization-insight-applications/
https://developer.cisco.com/meraki/api-v1/create-organization-insight-monitored-media-server
This one gets data for a monitored application...
https://developer.cisco.com/meraki/api-v1/get-network-insight-application-health-by-time/
Whether it'll give you what you want is another matter, you'll need to analyse/interpret.
Thousand Eyes mentioned by @PhilipDAth is way more powerful, if you need to understand and actively manage performance it's worth a look, you can get a free trial, it's easy to integrate with Meraki to do some testing.