Google prefers a LCP <2.5s which is hard to reach for phones from the Stone Age with 4G throttling and CMS with a lot of of js.
You still could try to enhance the server capabilities to reduce TTFB, to deliver locally and pipeline ALL css and js files. If the host is quick, it's quicker than CDN.
The js is most awful. 1kb js is always times more dreadful than 1kb of anything else. I tried to rebuild jquery with grunt but there always something from the jquery that was needed by zen cart. So no possibilities there and still one of the best js collection libraries.
Your shop is loading various of images. Though the main imag is >80kb thats's not too bad.
But you have lots of thumbnail images. All these want to be exeuted by the fucky js
And mobile has even more of that to handle menu etc.
roller-aus-blech.de
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