Plane Look at Camers script, help needed

Unity Engine
1

Hi,

My script is fully functional, but what i want to do is, instead of allowing my billboard to face camera by completely turning, i only want it to turn a maximum of 15 degrees left and right…

Like if i am in front of the plane, the angle of plane will be eith 90 or 180 or 360, what i want is it should maximum turn left or right to 15 degrees…

how can i achieve this ?

This is my script below -

using UnityEngine;
using System.Collections;
 
public class Billboard : MonoBehaviour
{
	Camera referenceCamera;
 
	public enum Axis {up, down, left, right, forward, back};
	public bool reverseFace = false; 
	public Axis axis = Axis.up; 
 
	// return a direction based upon chosen axis
	public Vector3 GetAxis (Axis refAxis)
	{
		switch (refAxis)
		{
			case Axis.down:
				return Vector3.down; 
			case Axis.forward:
				return Vector3.forward; 
			case Axis.back:
				return Vector3.back; 
			case Axis.left:
				return Vector3.left; 
			case Axis.right:
				return Vector3.right; 
		}
 
		// default is Vector3.up
		return Vector3.up; 		
	}
 
	void  Awake ()
	{
		// if no camera referenced, grab the main camera
		if (!referenceCamera)
			referenceCamera = Camera.main; 
	}
 
	void  Update ()
	{
		// rotates the object relative to the camera
		Vector3 targetPos = transform.position + referenceCamera.transform.rotation * (reverseFace ? Vector3.forward : Vector3.back) ;
		Vector3 targetOrientation = referenceCamera.transform.rotation * GetAxis(axis);
		transform.LookAt (targetPos, targetOrientation);
	}
}

I mean i dont want this to happen

I want it to turn max 15 degrees both sides from its base angle and only in the X - AXIS

2

I think i can do it if i can change this line

transform.LookAt (targetPos, targetOrientation);

to something like

transform.LookAt(Vector3(targetPos.x,targetPos.y,targetPos.z),targetOrientation);

but this line gives me error, i think this way i can reduce the percentage of turning for my x axis

what do you think ?