Let me get this straight. You are loading a document that has its images location online? Is there a specific reason for that option? To be honest, when I was using MSO in both industry and education, I never heard of that being done. From my point of view with working with documents that contain images, it would be better to have the images stored locally, instead of having to go online to deal with loading them.
Now here is an option to look at that might help it a little. It involves the "many pictures" part of your description of the document.
Go to Tools>Options>Memory
You will need to increase the "Graphics cache" options.
Increase the "Use for LibreOffice" to its max of 256 MB.
Increase "Memory per object" to 20 MB or more.
Increase "Remove from memory after" to double the amount of time you think you will be spending on editing the document.
Then increase the "Number of objects" to 10 or 20 more than the number of images you have in your document.
This will help keep the images viewed and on your local system, instead of needing to go mack to the online source[s] to re-view the images withing you document.
The load times may be reduced somewhat by this, hopefully.
As for the single/multi "GET" part of the loading of the document, I have no idea what the internals are for LO. I just use it and make some English Dictionaries/Thesaurus extensions for it.
.