Makes it sense to compress images before we load/import them into TB/Presta?
Not really. Currently even the "original" image gets rewritten on import[1], so such optimization doesn't survive the minute you add the image.
If you want well optimized images, add all of them, then run this optimizer on all the images in img/p/. Like downloading this folder via FTP, then optimizing, then re-uploading the result via FTP. Thirty bees won't touch these images and serve them happily as long as they exist and as long as nobody starts a "thumbnail regeneration".
Adding images later requires repeating this procedure for just the new images, of course.
[1] This is known and considered to be a mis-feature, but as always, somebody has to rewrite this code section, which didn't happen, yet.