Just closing this off with a solution - thanks for the tips.
The solution came from this post > Lazy Loading iframes - #4 by Pathfinder
I used the data-vimeo-defer option in each Vimeo iframe (18 in total x3 layouts) This had the effect of reducing the network calls to/from vimeo from +500 down to less than 50 drastically reducing the page load time and improving performance.
<iframe loading="lazy" data-vimeo-defer src="https://player.vimeo.com/video/148751763?badge=0&autopause=0&player_id=0&app_id=58479" frameborder="0" allow="autoplay; fullscreen; picture-in-picture" allowfullscreen title="You'll never guess what this video is!" ></iframe>
Note: For this to work the vimeo embed code must be inside a HTML widget in Hype rather than a rectangle object.