CPU Usage 100% on GO server

Hi,
Our clients just upgrade from NAV 5 to NAV 2015, and they are using GraphON to connect to NAV.
The GraphON server spec is :
- Windows server 2012 R2 (64 bit)
- Dual processors, each 4 cores 2.4 GHZ
- Memory 32GB
- Applications installed there : GraphOn server, Nav Client, Ms Office

Now the CPU usage is always high (99% all the time) with 50-70 users connect simultaneously.
The application server CPU usage is normal (around 60-70%).
When using NAV 5, we also using GraphON, but the CPU usage is normal.
Is this normal behaviour with NAV 2015?
The GraphON tech said its because NAV client is 32bit application, used in windows 64bit. Is this true?

What should we do to solve this?
Thanks