molotow

Defer Media is a plugin for speed up your website and defer not needed medias which out of the screen when page loaded. 
Then, when you scroll down the page, it will load images/videos/iframes automatically or pre-load it even if it it not visible yet (can be adjusted with Appearance Offset parameters).
This plugin will apply the following actions: 
– Defer images (standard [img] tag and also [picture] src sets) 
– Defer background images (if style=”background-image” applied for some block) 
– Defer Videos ([video], [source] tags) 
– Defer Youtube embedded videos (iframe) 
– Defer any Iframes ([iframe] tag)
You can see plugin demo on this page: 
<a href="https://joomcar.net/wp-optimize/a-lot-of-media-page/" rel="nofollow ugc">Defer Media demo</a>

Defer Media

This plugin defer images and videos loading on your site for make it faster

activity-log.com

Plugin allow you to run most important test for performance: request time, number of database queries, memory usage
You will be able to detect plugin which cause troubles and result with longer waiting time for request results
Testings are executed based on your homepage
<iframe loading="lazy" title="WordPress Profiler – What Slowing Down Your WP" width="750" height="422" src="https://www.youtube.com/embed/3hJbClFbw5s?feature=oembed" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>
How to use it?
In Dashboard go to Tools->Profiler What Slowing Down
Click on run test on all plugins (first link) and then near wanted plugin, run few tests and compare results
If you get significantly lower results, means that this plugin causing slowness
Hint: Lower numbers are better, means that page load faster without this specific plugin

Profiler – What Slowing Down Your WP

Plugin allow you to run most important test for performance, request time and number of database queries With this Plugin Performance Profiler you wil …

Defer Media vs Profiler – What Slowing Down Your WP