Somebody sends me a site and says it is slow. I open it, watch the network tab fill up, and there it is. Eleven photos. Six megabytes each. Straight off an iPhone, uploaded at full size, displayed in a box 400 pixels wide.
That is not a hosting problem. That is not a plugin problem. That is 66 megabytes of photograph being shipped over LTE to somebody sitting in their truck.
The math nobody does
A decent target for a whole page, everything included, is under two megabytes. Under one is better.
One unoptimized photo blows through that by itself. So the page is not slightly over budget. It is thirty times over budget, and the fix costs nothing but ten minutes.
What actually to do
Resize before you upload. Nothing on a normal website needs to be wider than about 2000 pixels, and most things need half that. Your phone shoots 4000 and change. Cut it down.
Convert to WebP. At around 80 percent quality your eye cannot tell the difference and the file drops by more than half. Every modern browser supports it. There is no reason left not to.
Let images below the fold load lazily, so the browser fetches them when somebody scrolls down instead of all at once on arrival.
And put real width and height on them. When the browser knows the size in advance the page stops jumping around while things load, which is the thing that makes people misclick and leave.
The one that gets missed
Your hero image. The big one at the top. That is the single heaviest thing on most sites and it is also the first thing anybody sees, which means it is doing double damage.
Get it under 200 kilobytes. Serve a smaller version to phones. If you cannot get it small enough and still look good, consider whether a giant photo is really what the top of your page needs.
Then stop
Fix the images and measure again before you buy anything else. I have watched people spend money on caching plugins and CDN upgrades and premium hosting when the whole problem was a gallery page.
Do the free thing first. The free thing is usually most of it.