The shaking can be changed from altering the setvelocity values. i.e. altering the numbers in bold
_shaken setvelocity[ -30+(velocity _shaken select 0)+random 60,-30+(velocity _shaken select 1)+random 60,-30+(velocity _shaken select 2)+random 60 ]
Decrease these values to decrease the amount of shaking. I'd reccomend keeping the first number half the second within the component like it is already (30 is half 60).
If it helps you understand this part of the code the script takes the x, y and z components of the velocity and adds between -30 and 30 to them.