It was good on OES 2015 SP1.
It got slow on OES 2018 and OES 2018 SP1.
Since Microfocus branded netstorage in blue.
Did you grow RAM on this upgrade?
I found that OES 2018 does use somewhat more RAM than before, and things that fall into swap are a bit sticky in there. So check how much of swap is being used, and perhaps looking at upping your RAM if swap is being used much. SP2 that has come out since you posted has helped some on this front, so make sure it is applied.