Grid layout lags after thousand inserts.

Hello everyone,

I'm trying to make a table using a grid layout. There are many tutorials on youtube showcasing how to do it and I basically insert a prefab white image with altered text whenever I need to populate a table. I also added a vertical scroll to be able to scroll each tab. Furthermore I added a toggle and a button script on each tab using RectTransform.SetAsLastSibling() to bring the respective tab in front.

The problem is that after a few hundred insertions on a tab the performance drops dramatically. At about 1000 insertions the table because sluggishly slow and is not good for use.

This is the code for the insertions (It's based on a postgres npgsql dll plugin)

 using System;
 using System.Collections.Generic;
 using UnityEngine;
 using Npgsql;
 using UnityEngine.UI;

 public class DBConnection : MonoBehaviour
 {
     private NpgsqlConnection conn;
 
     public bool Connected=false;
 
     // Start is called before the first frame update
     void Start()
     {
         
     }
 
     // Update is called once per frame
     void Update()
     {
         //should check here if the connection is active or down
     }
     public void Connect_Database()
     {
         // connection config
         string server = "****";
         string port = ""****";
         string database = ""****";
         string user = ""****";
         string password = ""****";
 
         // connection string format
         string connstring = String.Format($"Server={server};" +
             $"Port={port};" +
             $"Database={database};" +
             $"User Id={user};" +
             $"Password={password};");
 
         // attempt to connect to database
         Debug.Log("Connect String = " + connstring);
         try
         {
             // Making connection with Npgsql provider
             conn = new NpgsqlConnection(connstring);
             Debug.Log("Connected" + conn);
             
             conn.Open();
             Debug.Log("connection established");
 
             Connected = true;
         }
         catch (Exception e)
         {
             Debug.LogError($"Could not establish a connection, reason:{e}");
             Connected = false;
 
             throw;
         }
     }
 
     public List<string> Select_Pelatologio()
     {
         string sql = "SELECT * FROM Πελατολόγιο";
         return Select_Query(sql);
     }
 
     public List<string> Select_Peristatika()
     {
         string sql = "SELECT * FROM Περιστατικά limit 800";
         return Select_Query(sql);
     }
 
     public List<string> Select_Query(string query)
     {
         List<string> result_query = new List<string>();
         NpgsqlCommand cmd = new NpgsqlCommand(query, conn);
 
         NpgsqlDataReader dr = cmd.ExecuteReader();
         Debug.LogFormat($"Attempting to run query:{query}");
 
         // insert all items into the grid
         while (dr.Read())
         {
             string tmp = "";
             for (int i = 0; i < dr.FieldCount; i++)
             {
                 //tmp = ;
                 tmp += ($"{dr[i].ToString()}\t");
                 result_query.Add(dr[i].ToString());
             }
 
             Debug.Log($"{tmp}\n");
         }
         Debug.Log("Query finished");
         
         dr.Close();
         
         return result_query;
     }
 }

The grid code is this:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class Grid_Pelatologio : MonoBehaviour
 {
     public GameObject Prefab;
     //public int NumberToCreate;
     public GridLayoutGroup GridLayoutGroup;
     public GameObject Content;
 
     // Start is called before the first frame update
     void Start()
     {
         Clear_All();
     }
 
     void Update()
     {
 
     }
     public void Clear_All()
     {
         foreach (Transform child in this.transform)
         {
             Destroy(child.gameObject);
         }
     }
     public void Add_Random_Color(GameObject obj)
     {
         obj.GetComponent<Image>().color = Random.ColorHSV();
     }
 
     public void Insert_Items(List<string> items)
     {
         for (int i = 0; i < items.Count; i++)
         {
             GameObject obj = Instantiate(Prefab, Content.transform);
             obj.GetComponentInChildren<Text>().text = items[i];
         }
     }
     public void Insert_Item(string item)
     {
         GameObject obj = Instantiate(Prefab, Content.transform);
         obj.GetComponentInChildren<Text>().text = item.ToString();
     }
     IEnumerator ChangeGridSize(int x, int y)
     {
         yield return new WaitForSeconds(2);
         // Now do your thing here
     }
 }

What am I doing wrong? Thanks for your time and I'll gladly answer any specifications you ask.