Slow app when exporting CombinedGaze data into a Json file using Unity

Hello everyone,

I am trying to export the CombinedGaze data to a json file. I made this script, and it works. The problem is that the application turns to run super slow, and I don't know why. Any ideas?

using System.Collections.Generic;
using UnityEngine;
using HP.Omnicept.Unity;
using HP.Omnicept.Messaging.Messages;
using System.IO;

public class WriteGazeData : MonoBehaviour
{
    [System.Serializable]
    private struct MyAppGD
    {
        public List<Vector3> rateValues;
    }

    public float timer;
    public bool dataExported;

    public string filename = "GazeData_FirstExperiment.json";
    private MyAppGD myAppGD;
    private GliaBehaviour _gliaBehaviour;
    private GliaBehaviour m_gliaBehaviour
    {
        get
        {
            if (_gliaBehaviour == null)
            {
                _gliaBehaviour = FindObjectOfType<GliaBehaviour>();
            }

            return _gliaBehaviour;
        }
    }
    private string savePath
    {
        get
        {
            return $"{Application.streamingAssetsPath}/{filename}";
        }
    }

    #region Unity LifeCycle

    private void OnEnable()
    {
        m_gliaBehaviour.OnEyeTracking.AddListener(HandleGD);
    }

    private void OnDisable()
    {
        m_gliaBehaviour.OnEyeTracking.RemoveListener(HandleGD);
    }

    private void Start()
    {
        myAppGD = new MyAppGD { rateValues = new List<Vector3>() };
        dataExported = false;
    }

    private void Update()
    {
        timer -= Time.deltaTime;

        if (timer < 0 && dataExported == false)
        {
            Debug.Log("Data was exported");
            SaveToJson();
            dataExported = true;
        }
    }
    #endregion

    private void HandleGD(EyeTracking gd)
    {
        if (gd != null)
        {
            myAppGD.rateValues.Add(new Vector3 (gd.CombinedGaze.X, gd.CombinedGaze.Y, gd.CombinedGaze.Z));
        }
    }

    private void SaveToJson()
    {
        string json = JsonUtility.ToJson(myAppGD, true);
        File.WriteAllText(savePath, json);
        Debug.Log($"Saved values at: {savePath}");
    }
}