How can I generate procedural 3D geometry faster?

In my game I have 3D grids that are generated then the y positions of the vertices are displaced to perlin noise, which makes terrain which has to be loaded in chunks. Currently I have the grid loading in chunks, the player can go in every direction infinitely and the way I do this is by removing the 3 chunks behind you and instantiating 3 chunks in front of you. This would be ok, if it didn't take ten seconds to make the 3 chunks in front of you. How can I generate the chunks faster? I have experimented with not using perlin noise, which I thought was what was making it slow, but it didn't make a difference. Here's my code for generating the chunk, which are instantiated in another script. (well, its not really my code)

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class MeshTerrain : MonoBehaviour {
 
     public int sizeOfChunk = 128;
     private int size;
     private int length;
     public float spacing = 1;
     public MeshFilter terrainMesh = null;
 
     public int eMid = 2;
     public int sMid = 5;
     public int eHigh = 5;
     public int sHigh = 10;
     public int eLow = 1;
     public int sLow = 5;
     public int eMacro = 2;
 
     public int eTemp = 10;
     public int sTemp = 2;
     static int tempRandomiser = Random.Range (0,10000);
 
     public int ePrecip = 10;
     public int sPrecip = 2;
     static int precipRandomiser = Random.Range (0,10000);
 
     static int randomiser = Random.Range(0,10000);
 
     // Use this for initialization
     void Start () {
         size = sizeOfChunk + 3;
 
         if (terrainMesh == null)
         {
             Debug.LogError("ProceduralTerrain requires its target terrainMesh to be assigned.");
         }
         GenerateMesh();
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 
     //this part generate terrain
     float GetHeight (float x, float z){
         float height;
         float heightA = Noise.Noise.GetNoise((x+transform.position.x) / sMid + randomiser,0, (z+transform.position.z) / sMid + randomiser) * -eMid;
         float heightB = Noise.Noise.GetNoise((x+transform.position.x) / sHigh + randomiser,0, (z+transform.position.z) / sHigh + randomiser) * -eHigh;
         float heightC = Noise.Noise.GetNoise((x+transform.position.x) / sLow + randomiser,0, (z+transform.position.z) / sLow + randomiser) * -eLow;
 
         float heightM = Noise.Noise.GetNoise((x+transform.position.x)  + randomiser,0, (z+transform.position.z)  + randomiser) * -eMacro +800;
 
         //float temperature = Noise.Noise.GetNoise((x+transform.position.x)/1.2f+ tempRandomiser,0, (z+ transform.position.z)/1.2f + tempRandomiser) * eTemp;
         //float precipitation = Noise.Noise.GetNoise((x+transform.position.x)/1.2f+ precipRandomiser,0, (z+ transform.position.z)/1.2f + precipRandomiser) * ePrecip;
         height = heightA + heightB + heightC + heightM;
         //Debug.Log (precipitation);
         //if(precipitation >= 10 && temperature <= 10){
         //    height -= 10;
         //}
         return height;
     }
 
     void GenerateMesh ()
     {
         List<Vector3[]> verts = new List<Vector3[]>();
         List<int> tris = new List<int>();
         List<Vector2> uvs = new List<Vector2>();
 
         for (int z = 0; z < size; z++)
         {
             verts.Add(new Vector3[size+1]);
             for (int x = 0; x < size; x++)
             {
                 Vector3 current_point = new Vector3();
                 current_point.x = (x * spacing);
                 current_point.z = z * spacing;
                 
                 current_point.y = GetHeight(current_point.x-1, current_point.z);
                 
                 verts[z][x] = current_point;
                 //uvs.Add(new Vector2(x,z)); 
                 if (x-1 <= 0 || z <= 0 || x >= size)
                 {
                     continue;
                 }
                 // Generate the triangle north of you.
                 tris.Add(x + z*size);
                 tris.Add(x + (z-1)*size);
                 tris.Add((x-1) + (z-1)*size);
                 tris.Add((x-1) + z*size);
                 tris.Add(x + z*size);
                 tris.Add((x-1) + (z-1)*size);
             }
             
             // Unfold the 2d array of verticies into a 1d array.
             Vector3[] unfolded_verts = new Vector3[size*size];
             int i = 0;
             foreach (Vector3[] v in verts)
             {
                 v.CopyTo(unfolded_verts, i * size);
                 i++;
             }
             
             // Generate the mesh object.
             Mesh ret = new Mesh();
             ret.vertices = unfolded_verts;
             ret.triangles = tris.ToArray();
             //ret.uv = uvs.ToArray();
             
             // Assign the mesh object and update it.
             ret.RecalculateBounds();
             ret.RecalculateNormals();
             terrainMesh.mesh = ret;
 
         }
     }
 
 }
 

So, how can I make this faster? Is there something here which is slowing down the game or do I need to try a different method?