Hi @MDevTeam3,
you could try adding this script to your post template
{% require_head %}
<link rel="preload" as="image" href="{{ content.featured_image }}">
{% end_require_head %}
As for optimization: What’s the filesize of the image(s)?
If you haven’t already - here’s the documentation about {% require_js %} which might be benefitial
best,
Anton