ARIS 9.8 memory usage

Since a few days we are finally running ARIS 9.8 instead of ARIS 7.2

A complete new server, having 8GB internal memory. But that memory is constantly loaded for 98%, giving a poor and unstable performace. Anyone an idea what could be wrong? We are using ARIS concurrently by 4 persons. No connect (we use ProcessWeb on an other server).