Image Viewers scrolling speed comparison
Windows Photo and Imagine have nearly instant reaction. At the end of Imagine I was pausing myself. Imagine, though, has very slow file browser. Sometimes hanging for minutes when opening large folders. Windows Photo doesn't have file browser and folder scrolling only works with Windows File Explorer.
XnView MP and IrfanView are both average. Irfan has very basic file explorer.
FastStone viewer is just slow as hell. Spending seconds on opening phone camera JPEG files.
Imagine and Windows Photo are totally free. XnView MP, IrfanView and FastStone are free for home use only.
Pictures are 16-megapixel JPEGs 5,5 MB in average.