First of all: I do not write native English 
My story: Naive as I was, I ordered the Echo Show 15 to use as my home assistant dashboard. Unfortunately, no APPs, no Fully Kiosk browser and keeping the HA panel open only worked via a custom skill which was restarted every 5 minutes by an automation.
When I read more on the internet, I found out that the HA panel can be kept open by permanently playing a video.
But unfortunately the Echo Show 15 blocked the automatic playback of videos. After a lot of back and forth, I finally found a solution, also with the help of this forum, so that I have now managed to play a video in the loop and autoplay.
Ultimately, this post put me on the right track:
Thanks to tom-x1
For this I use the “index.html” now in a slightly modified form. It was important to somehow achieve that the loop function also takes effect.
<html>
<head>
<script src="https://vjs.zencdn.net/5.6.0/video.js"></script>
<link href="https://vjs.zencdn.net/5.6.0/video-js.css" rel="stylesheet" />
<script src="https://unpkg.com/videojs-abloop/dist/videojs-abloop.min.js"></script>
</head>
<body>
<video autoplay="" muted="true" id="vid" controls class="video-js" width='480' height='270' >
<source src="http://XX.XX.XX.XX:8123/local/video/world.mp4" type='video/mp4'>
</video>
<script>
var video = videojs("vid",{
plugins: {
abLoopPlugin: {}
}
});
video.ready(function(){
this.abLoopPlugin.setStart(1).setEnd(29).playLoop();
});
</script>
</body>
</html>
To embed the video in Lovelance I use an iframe and set the size to 0%, so it is no longer visible. Probably you have to embed it for each room/tab.
type: iframe
url: http://XX.XX.XX.XX:8123/local/video/index.html
aspect_ratio: 0%
If someone finds a more elegant solution to this, or can improve it here, then happy to reply to this post
