Three causes account for most slow websites, in this order: images that were uploaded straight from a camera, third-party scripts nobody audits, and hosting that is oversold. Everything else is a rounding error until those are dealt with, and most speed advice online concerns the rounding errors.
Images
A photograph from a phone is four to eight megabytes and around 4000 pixels wide. It is displayed in a box 800 pixels across. The browser downloads all of it and then throws most of it away. Ten such images on a page is forty megabytes for a visitor on mobile data, and on a Pakistani connection that is not a slow page, it is a page nobody waits for.
The fix is resizing and compressing on upload, serving modern formats, and loading images below the fold only when they are needed. A site doing all three routinely drops its page weight by eighty percent without a single visible difference.
Third-party scripts
Every embedded chat widget, analytics tag, heatmap, advertising pixel and font service is a request to somebody else's server that your page waits for. Each was added for a reason and most of those reasons expired. Auditing what is loading, and removing what nobody has looked at in a year, is usually the second largest win available and costs nothing.
Hosting
Shared hosting means your site shares a machine with hundreds of others, and a busy neighbour is your problem too. That is a reasonable trade for a small site and a poor one for a store. Before paying for an upgrade, check whether the response time is slow consistently or only at peak, because the second pattern points at the neighbours and the first at the code.
What matters less than the internet says
Minification, combining files and shaving milliseconds off a script are real but small, and they are what most speed reports lead with because they are the easiest to measure automatically. Fixing them on a site serving forty megabytes of images is rearranging the furniture while the roof is off.
How to check honestly
Test on a mid-range Android phone on mobile data, not on your desktop on office broadband. The gap between those two is the gap between what you experience and what your customers do.
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