Desktop Will Never Utilize Enough Ram it Uses Less as the Encoding is going.

I have to encode video a lot and the ram is never utilized enough it takes so long to run a video through. The computer has Two (Intel(R) Xeon(R) CPU E5-2620 v4 @ 2.10GHz, 2101 Mhz, 8 Core(s), 16 Logical Processor(s)) and 32GB of ram but the Media Encoder never uses more than 15GB with the memory preference set at 28gb. As the video encodes the ram usage goes down but never up.