SQL is slower straight after creating the DB, This occurs because of AutoGrow

sqlSlower

using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication8
{
    class Program
    {
        static void Main(string[] args)
        {
            int iterations = 10000;

            var cnn = new SqlConnection("Data Source=localhost\\sqlexpress;Integrated Security=True;");
            cnn.Open();

            var createCmd = new SqlCommand();
            createCmd.Connection = cnn;

            createCmd.CommandText = "if exists(select * from sys.databases where name = 'test-db') drop database [test-db]";
            createCmd.ExecuteNonQuery();

            createCmd.CommandText = "create database [test-db]";
            createCmd.ExecuteNonQuery();

            createCmd.CommandText = "create table [test-db].[dbo].TestEntities(Id int primary key, TestDate datetime, TestInt int, TestString nvarchar(512))";
            createCmd.ExecuteNonQuery();

            var insertCmd = new SqlCommand();
            insertCmd.Connection = cnn;
            insertCmd.CommandText = "insert [test-db].[dbo].TestEntities(Id , TestDate , TestInt, TestString) values(@Id, '2012-1-1',423423,'543254gddvfcsa')";
            var idParam = insertCmd.Parameters.Add("@Id", System.Data.SqlDbType.Int);


            Stopwatch timer = new Stopwatch();

            timer.Restart();
            using (var t = cnn.BeginTransaction())
            {
                insertCmd.Transaction = t;

                for (int i = 1; i <= iterations; i++)
                {
                    idParam.Value = i;
                    insertCmd.ExecuteNonQuery();
                }
                t.Commit();
            }

            timer.Stop();

            Console.WriteLine(timer.ElapsedMilliseconds);

            var truncateCmd = new SqlCommand();
            truncateCmd.Connection = cnn;
            truncateCmd.CommandText = "truncate table [test-db].[dbo].TestEntities";

            truncateCmd.ExecuteNonQuery();

            timer.Restart();
            using (var t = cnn.BeginTransaction())
            {
                insertCmd.Transaction = t;

                for (int i = 1; i <= iterations; i++)
                {
                    idParam.Value = i;
                    insertCmd.ExecuteNonQuery();
                }

                t.Commit();
            }
            timer.Stop();
        
            Console.WriteLine(timer.ElapsedMilliseconds);
        
            cnn.Close();
        }
    }
}