Images play a huge roll when it comes to any site performance.
Uploading perfectly compressed and well balanced images can very time consuming.
Try these simple ssh commands to compress GIF's, PNG's and JPG's from pub/media folder.
Use it with caution because some images can be extremelly compressed and visually ugly.
find ./pub/media -iname '*.gif' -exec sh -c 'gifsicle -b -O3 -o "{}.out" "{}"; mv "{}.out" "{}"' \;
find ./pub/media -iname '*.png' -exec optipng -o5 -keep -preserve '{}' \;
find ./pub/media -type f -iname '*jpg' -exec sh -c 'jpegtran -outfile "{}.out" -optimize "{}"; mv "{}.out" "{}"' \;