I had this same issue recently with a client complaining about slow loading times when users tried to play modules from within their offices.
The SCORM files were on SCORM Cloud, so we new the issue was NOT with the LMS. It was simply that the client's own internet bandwidth was far too limited and clogged up with lots of other bandwidth-hogging apps. People accessing the same courses on SCORM Cloud from home computers had very fast load times.
So I would suggest you investigate your internal internet bandwidth. It could be that the IT department has 'throttled' the bandwidth allowed for browser-related content or anything it sees as being video.
If IT tells you they have gigabit ethernet and bandwidth is NOT an issue, don't believe them. Whatever bandwidth they have available will ALWAYS BE SHARED among all users and all apps being used. Some apps (e.g. enterprise systems) will have priority over anything related to training.