Marketplace HTML page load time is lengthy, in part because images are sent inline, not pulled asynchronously and cached. Revise portal so solution images can be fetched by URL, instead of embedding the images in the page as data, and cached by the browser.
Browsers can fetch multiple items in parallel and cache large items like images. Most web sites take advantage of this by pushing out HTML that has IMG tags with links to the site, so the browser can fetch the images asynchronously. You see this as a web page loads its text first, then adjusts as the images trickle in.
I guess the portal could implement an open get-image endpoint at a URL like solution/abc123-id-abc123/image, which would call an appropriate CDS endpoint.