Just to clarify my prior comments, I was not sure if the module/plugin supported clustering at all, and my remote suggestion/diagnosis was that if 100k markers were trying to be rendered on a single embedded map, this would surely crash.
Sounds like 1) Omeka Classic module DOES have clustering built in, and 2) Omeka-S does it differently (so conceivably, never outputs 100k markers to be rendered, but not through clustering).
My comments did not apply to a system-wide slowdown on other pages outside of the map embed page I agree with Jim it’s not likely it would impact installation across the board.
One remote possibility that I recently encountered is that certain JS includes that are coming from outside the main server (jquery, something in the theme, even something in the plugin) could be having a delay in loading due to - many factors. It’s easy to diagnose with the “Inspect / Developer Tools” feature in any browser. The “Network” view in Firefox or Chrome, for instance, will let you view each individual file object being loaded, and whether it was successful. If you need help finding or interpreting this, feel free to post a URL and me or someone else knowledgeable can take a look!