GTMetrix is telling me:

The following inline script blocks were found in denver process servers.net/ between an external CSS file and another resource. To allow parallel downloading, move the inline script before the external CSS file, or after the next resource.

Inline script block #1
The following external CSS files were included after an external JavaScript file in denver process servers.net/. To ensure CSS files are downloaded in parallel, always include external CSS before external JavaScript.

denver process servers. net/css/main.css

Is there even any way of optimizing these, in RSD 2.5?

As far as I can see, there are no external css or js files on your site. Whether 'external' in RSD has a different meaning than for the GTMetrix I don't know.
But it might mean that there are two js files between the block of css files and the main.css. If it were possible to move main.css up before those two, maybe GTMetrix would be satisfied. There is nothing you can do about that within RSD2.5. It would have to be done after export - EVERY export. But then again, I don't know if that would cause an avalanche of other problems. You simply have to ask CC support about it.