Thank you for using Neve.

As far as I know, the theme does not generate copies of images to produce different formats thus it just uses the post’s featured image based on the layout and space available on the blog/archive page. The easiest way to force the same image size for the posts’ thumbnails will be to use a smaller one, for example the exact size of 150×150. Please note this may affect how the image looks on the single post layout, but it can be hidden on this type of page if you want to – https://docs.themeisle.com/article/1310-neve-single-post-options#single-post-page-elements.

I hope this will help.