Any way to display the Large Size image not the Full Size?

Any way to display the Large Size image not the Full Size?

Very important for page speed load times. I prefer not to use image downsizing when uploading. Using multiple custom post thumb sizes does the trick while retaining the originals in hi res.

Also, when the images are a bit too large, it slows the swipe down a lot.

https://www.ads-software.com/plugins/responsive-image-gallery/