I have to rotate my unit to look at where I click my mouse.

I’m currently using a Quaternion.Slerp function to rotate my unit. However, it takes the same amount of time to rotate 90 degrees, as it does 180 degrees.
If it takes 2 seconds to rotate 180 degrees I only want it to take 1 second to rotate 90 degrees.

Do I have to create logic to change the speed at which I rotate, or is there a better function or something etc to do this?

Plane plane = new Plane(Vector3.up, 0);
float dist;
void Update () {
//cast ray from camera to plane (plane is at ground level, but infinite in space)
Ray ray = Camera.mainCamera.ScreenPointToRay(Input.mousePosition);
if (plane.Raycast(ray, out dist)) {
Vector3 point = ray.GetPoint(dist);
//find the vector pointing from our position to the target
Vector3 direction = (point - transform.position).normalized;
//create the rotation we need to be in to look at the target
Quaternion lookRotation = Quaternion.LookRotation(direction);
float angle = Quaternion.Angle(transform.rotation, lookRotation);
float timeToComplete = angle / rotationSpeed;
float donePercentage = Mathf.Min(1F, Time.deltaTime / timeToComplete);
//rotate towards a direction, but not immediately (rotate a little every frame)
//The 3rd parameter is a number between 0 and 1, where 0 is the start rotation and 1 is the end rotation
transform.rotation = Quaternion.Slerp(transform.rotation, lookRotation, donePercentage);
}
}

The idea is to calculate the rate of changing from 0 to 1 in the last argument of Slerp, since that is the percentage of desired transition, 0 is starting rotation and 1 is rotation we end up with.