What loads on a VDP
Each part often comes from a different company: the gallery from the photo vendor, the price from the inventory feed, the calculator and trade-in tool from their vendors, and chat from another. All of them start when the page opens.
Photos: the first one fast, the rest later
The first photo is what the shopper came to see, and most often the element Largest Contentful Paint measures, so it should load immediately and at the size of the screen. The rest of the gallery should load as the shopper swipes, not all at once. See lazy loading vehicle photos.
Test it on a phone
Many VDP visits come from ads and search, on phones. Test two or three different vehicles, one with many photos and one with few, on a phone over a cell connection, and in the free speed test.
Let the tools wait their turn
The payment calculator, trade-in tool and chat matter, but not before the shopper has seen the vehicle. Site Speed Engine loads the photo, price and lead form first, and the tools right after.