Very slow multiscatter vs native geo(mesh)

[perry2016]

We work with Vray 3.57.01 in Max 2014 on a intel E5-2699-V3 (72 cores) based computer (128 gb ram)
Multiscatter is very slow compared to native max geo(just a mesh), see the test results below and see the images:

• render the native max geo it takes 0min42sec,
• render the multiscatter geo it takes 3min20sec.

Why??

according to iCube R&D Group it is a Vray problem, not multiscatter....