There is a problem with Google PageSpeed Insights. You can, ironically, Google "why PageSpeed Insights doesn't matter" and find numerous posts like these:
PageSpeed Insights doesn't actually measure page speed, but uses a kind of checklist to show which elements you have implemented. Some of those, like "cache-control", are counter-productive when the service is already using a Content Delivery Network (CDN) as a cache, as we do. It can force the browser to fetch the image new instead of from the cache provided by the service. Compressing assets is another area that will probably be counter productive because they are already delivered, via the CDN, from a close source to the viewer, and do not have to employ the use of the webserver to decompress again.
The one thing you can do is make sure your own images are optimized before uploading them and using them in your pages. There are other page speed services that will show which element has the longer loading time,
The items we can't do, because they are either counter-productive or impossible, are "leverage browser caching", "use a cache validator" (for the aforementioned reason) and "minimize redirects" (which would break your link tracking, open & click rates, etc.)