and every 15 seconds data will be going to the servers and stored, so a lot of data is transmitted
Have they considered programming the game better, then?

Although we won’t be able to expand inventory straight away, we want to make it more convenient to use retainers. So you can e.g. access all retainers in certain areas, rather than one by one.
Comments like this make me think they don't actually understand the problem at all.