Images and posts load slowly

Hi everybody! I am working on a website that uses the “Post Grid Plugin”. The client complains that the articles need a lot of time until they are visible. (Yes, I use a caching plugin, dont worry. 😉 )

My question is, if someone could tell me whether the loading time is normal or not. I am using a self coded theme based on a startertheme. I have only finished the desktop version yet, on smartphone the design is not ready. Here are the URLs: https://authentic-translation.com/blog-test https://authentic-translation.com/blog-test/page/2/

Thank you for having a look!
Raphael

The page I need help with: [log in to see the link]