The problem with that is it makes it even worse for those of us who don't want to deal with jars. At least when it was 125, I could loot everything and ignore that I got empty jars and they'd only take one slot until I hit 125. With only 15, I'd be using multiple slots very quickly in a POI, especially a tier 5 POI. Since I don't normally spend time looking at what I loot and just hit loot all for each container, I'd quickly end up with a bunch of slots filled with jars that I'd then have to drop in order to pick up other things when I got full. That's what I don't want to have to do again and one reason why I don't support adding empty jars back.
Unless you can't loot empty jars. If you want to say that you can't loot jars, then feel free to have them be a small stack size.
Even so, unless they make it so you have to fill each jar one at a time with a 2 second or so timer so that it's just a royal pain to do (but is immersive and realistic!!), then empty jars will always end up being extremely easy no matter how you set them up unless you limit the total number you can carry to only a few total - perhaps having a "canteen" slot that is the only way to carry a reusable water container (jar or canteen or bottle or whatever).