You are having kind of the opposite problem that I am. I had 64 GB RAM (3600 MHz, non-ECC) for the past 2 years, and BI would hover somewhere around 20-25 GB memory utilization. I upgraded to 128 GB ECC RAM (3200 MHz), and now it only uses 3-5 GB. Double the memory, and the the utilization is a fraction of what it was. Nothing else was changed. One of life's mysteries, I suppose.