Another way is to only show all upcoming sessions plus some number (0, 5, or 10) of past sessions. I have probably never looked back at sessions that have already been hosted since I cannot edit, duplicate, or delete them, making it useless to load them while editing the series. I can see all the sessions in the series directly on the series page anyways.

Also, I believe the problem is the page having to load the times, categories, and descriptions of hundreds of sessions, so segmenting the page into separately loaded sections of 50-100 each might fix the issue.

I believe it could be my problem as 100 session series also lag for me, but other people on laptops also seem to have this issue