How to optimize images for web | Photoshop
Image file size has to be optimized for web in order to have faster web load time. Check how you can lower the file size in Photoshop with "Safe for web" export function.
You also may use shortcut "Ctrl+Alt+Shift+S"
If the image quality is too bad after compressing (image is too pixelated), simple leverage the quality up in the export dialog until it is good enough again