So, there are a lot of factors that come into play when loading sites.
I tend to find, that external tools that are used to test site loading times, tend to add extra ‘loading time’ to mobile sites. Traditionally, because mobile sites take longer to load.
There are a few things that can be done to help with sitting loading time, such as reducing image quality (jpg tends to load quicker than png).
Site loading tools, often look at how quickly the whole page loads. I don’t know if other people do this, but I tend to worry more about how quickly a user can interact with the site, and what they see first. If an image at the bottom of the page hasn’t loaded straight away, then it can load in the background whilst the user scrolls through the page.
The order in which things load, is dictated by the site structure, and how it has been built.
In addition, mobile sites do take longer to load than desktops, because the processing power is lesser.
This blog post made by Wix, might help
https://www.wix.com/blog/2019/04/website-speed-optimization/
I hope this helps you.