I use to have an old pentium 2 computer for testing websites. Sometimes you cant make things fast enough for the old box. A fun trick is/was to have <script>elm.textContent="loading images"</script> between each "heavy" section, all targeting the same elm. If the computer, network or server is truly extremely slow you will get a nice message at the top describing what they are waiting for. On a normal slow computer you won't see the messages unless something went wrong.