Owncloud-client 2.3 slows down bandwidth to almost zero

I installed qt5-default, but still owncloud-client 2.3 does not let me limit the network speed.

The following issue [1] has all needed info which packages and QT5 versions you need to get this bandwith limiting functionality to work. Just installing a random package won't work as the client you're using also needs to be build against that package.