Articulate Storyline: Sluggish Courses?

3-9Mb is nothing, so no worries there.

497Mb is pretty big, but not so much as I would immediately think the size was the cause of all the issues.

Big high res video would definitely put a strain on your Learners devices, and if they are on slower internet speeds and/or older devices then the negative effect will be even larger.

So maybe you could reencode some of that video down to a lower bitrate. (or if your LMS allows, use the Streaming "adaptive" option in Storyline publish settings?)

So apart from the video, Im not entirely convined that the problem lies within your Storyline files themselves. Infact one thing you said at the start would make me think its the LMS - you said " the page not responding, documents connected to the course won't open, buttons in LMS do not load in."

This all sounds like LMS/server issues.

In that case, I would recommend trying out your course on ScormCloud. Its the industry standard LMS for testing purposes, and is very good at rooting out issues. (its also free for courses up to 100Mb!... so you'll need to resize down that 497Mb course in order to try it on the free version)
https://app.cloud.scorm.com/sc/guest/SignInForm

If possible, try to set up your test environment so it as absolute close as possible to the environment those Learners were using when tyhey reported problems. eg. if they are using slow internet, old machines, iPhone 6s etc - then you do the same.

Even better, maybe some of the Learners themselves can try the ScormCloud versions and see if they work better?