How large is your SCORM module overall?
First you need to understand the actual problem.. is it the image files that are taking a long time to be sent by the server? or is it the CSS or other things? You can use Google Chrome's developer tools to analyze it and see what the slow down is:
https://developers.google.com/web/tools/chrome-devtools/network-performance/
It also has a handy tool to simulate what it would feel like on dial-up or a mobile internet 2G/3G connection so you can see the impact it has.
It is quite possible your VPS doesn't have much bandwidth for sending large image files out and that's your bottleneck. Only way to get around that honestly is to pay more money for faster/more bandwidth on the server side or maybe looking into something like MoodleCloud?
You could also try to host your largest images/videos on another site and embed them. That way people are downloading it from that site (which may or may not have CDNs) rather than your one server. That's why people use YouTube or Vimeo for videos for example.