Another editor I used loaded the names of the opened files into the buffer ring, but did not load their content until needed -- e.g. content needed to be painted on the screen, or accessed in memory by a macro.
I think on startup SE completely loads all the files that were previously opened -- i.e. adds the file name to the buffer ring, and also loads the full content of the file.
But, look in Tools/Options/File Options/Load/Load entire file. The default is true, but maybe setting it to false might help your scenario.
Update: But I just tried setting "Load entire file" false, and using
Process Monitor confirmed that SE loads the entire files at startup either way. I'm not sure what the setting controls. Perhaps something in SE has changed and is accidentally defeating the setting. Or maybe it's a custom macro that's defeating it.