Drop fps unit creation

Hi,
I have an issue at the beginning of each game : fps between 150 et 200, but it drop at 20 for every new unit wich is created (hero, unit, water elemental, …). Is there a solution?
My config :
CPU : i5 6300 HQ
RAM : 8 Gb
GTX 950 M

config game :
full screen
1600x900
low
300 fps first plan
10 fps back plan
no shadow
low lighting
no foliage
no anticrenelage
no sync vert

When i use the classical graphics, i don’t have this issue.

Thanks