Json feed to cache – NOT working

my site taking json feed but it does not cache to load instantly, every time I load the page it loads the feed too and it takes time to load properly.

here is the page – https://popmellow.com/top-100-alternative-songs/

Please wait a while to load json feed properly you will get but m trying to say.

While this page json file loads instantly –
https://www.popvortex.com/music/charts/top-pop-songs.php