Slow at loading images of movies

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This could be an issue anywhere from network speed to cache (as you've mentioned) to ill-configured reverse proxy. Your question is too broad to provide more detail. Could you offer more information about your setup? Bare metal? Host OS? Server version? Clients where you experience the issue?

Best practice: run on the most capable hardware, always hard-wire the server (i.e., your laptop in this instance -- even WiFi could be the problem), and use an SSD to serve cache, even if you have to map the volume separately.