Banner fallback image slow loading on mobile

Site URL: https://www.cityzerofilms.com/

Hi folks,

Minor issue here.  I recently added our demo reel to autoplay in the Home page banner which will only work on desktop (would love it to work on mobile but...).  I then chose a fallback image for mobile.  The fallback image on mobile always takes a few seconds to load and I'm wondering if there's anything I can do to speed that up.

Things I've already tried:

Resized the image to 1365x768

Encoded the image export to JPG rather than PNG.

Any help is much appreciated.  Thanks!