Images increase in size after uploading into Media

it is a wordpress limitation : 2560px – all images bigger than that will be recalculated and saved as xyz-scaled.jpg ( or png etc )
– Enfold creates some image-formats for their used elements ( see functions.php line 185ff : sizes )
– on functions.php lines 246ff – you see that for these images a compression level is set to 100% – : no compression.

That is the reason why the original jpg ( with 2560px width) might be smaller in file-size as the recalculated 1500px image ( featured_large or extra_large ).
You can set this compression level by a small snippet in child-theme functions.php:
e.g. for compression level 55%:

add_filter("avf_jpeg_quality", "avf_set_quality_mod", 9999, 1);
add_filter("avf_wp_editor_set_quality", "avf_set_quality_mod", 9999, 1);
function avf_set_quality_mod($quality) { $quality = 55; return $quality;}

This will only influence the uploading process. If you want the existing images have the same compression level you might use a “regenerate Thumbnails” Plugin afterwards.

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PS: you can influence this big image threshold via a filter : big_image_size_threshold see here: Link
f.e.:

function increase_big_image_size_threshold( $threshold ) {
    return 3500; // new threshold
}
add_filter('big_image_size_threshold', 'increase_big_image_size_threshold', 999, 1);