Salesforce Lightning Performance

To view Page Performance by Browser and Other New Metrics in the Lightning Usage App, check this

Best Practices:
1. Avoid doing call out on the page load. You can use a Tabs component and add separate tab for displaying information from call out.

2. Update your browser regularly.

3. If you have added any Lightning components or Visualforce pages, make sure they are using all the Best Practices.

4. Use Salesforce Lightning Inspector Chrome Extension for checking the conformance and troubleshooting.