As far as I can see the loading speed is due to the servers and often happens when you import resources from an of-site source. I don't think it should be a problem for you since the instagram feed is quite far down the page and by the time you reach them they have loaded.
If it's possible, you can add inside the img tags for the instagram posts:
so the image becomes:
<img loading="eager" class="eapps-instagram-feed-posts-item-image es-post-media-image" src="https://scontent-iad3-1.cdninstagram.com/v/t51.29350-15/247280374_246122147569006_5054304244329752902_n.jpg?_nc_cat=100&ccb=1-5&_nc_sid=8ae9d6&_nc_ohc=6O1dUFuiBZMAX-W08XQ&_nc_ht=scontent-iad3-1.cdninstagram.com&edm=AM6HXa8EAAAA&oh=372c1688126c43d95df095ec511849ec&oe=619B040B" eapps-link="image" alt="back to nature, back to basics bYo Vibes 🧘🏻 #most #natural #yogamat...">
This could improve the loading speed of the images, but it might negatively affect your page loading speed overall.