A product page has more to do than any other template. It shows a gallery, calculates a price, checks stock, renders options, loads reviews and recommends related items. Every one of those is a chance to be slow.
Which is why the diagnosis matters: the same symptom has at least four different causes here, and they need different work.
Images, almost always
Product photography is the largest thing on the page by a wide margin. Stores upload at the resolution the photographer delivered, and the browser scales it down after downloading all of it.
- Serve the size that is actually displayed, not the original.
- Use a modern format. The saving over the same image as JPEG is substantial and visually invisible.
- Load the first image eagerly and the rest of the gallery lazily. The first one is your largest contentful paint and should never be deferred.
- Reserve the space before the image arrives, or the page jumps and you fail CLS.
Configurable products
A configurable product with several options and many variants has to give the browser enough data to update price, image and availability when someone picks a size. That data can get large.
A product with three options and a hundred combinations ships a table of a hundred rows before anyone touches anything. Rarely a problem on its own, frequently a problem in combination with everything else on the page.
Everything that is not the product
Reviews, recently viewed, related products, upsells, cross-sells, stock notifications, size guides. Each one is a reasonable feature and each one costs something.
The useful question is not whether to keep them but when they load. Anything below the fold can wait until the visitor scrolls, and most stores load all of it immediately because that is the default.
What we look at, in order
- Total image weight and format. Nine times out of ten the biggest win is here.
- What loads before the page is usable, versus what could wait.
- The variant data for configurable products.
- Third-party widgets, particularly review platforms, which often bring their own JavaScript.
- Server response time, because if that is slow none of the above is your first problem.