Currently I loaded all my assets in XNA in the main Game class. What I want to achieve later is that I only load specific assets for specific levels (the game will consist of many levels). Here is how I load my main assets into the main class:

protected override void LoadContent()
        {
            spriteBatch = new SpriteBatch(GraphicsDevice);

            plane = new Player(Content.Load<Texture2D>(@"Player/playerSprite"), 6, 8);
            plane.animation = "down";
            plane.pos = new Vector2(400, 500);
            plane.fps = 15;

            Global.currentPos = plane.pos;

            lvl1 = new Level1(Content.Load<Texture2D>(@"Levels/bgLvl1"), Content.Load<Texture2D>(@"Levels/bgLvl1-other"),
                new Vector2(0, 0), new Vector2(0, -600));

            CommonBullet.LoadContent(Content);
            CommonEnemyBullet.LoadContent(Content);
        }

        protected override void UnloadContent()
        {
        }

        protected override void Update(GameTime gameTime)
        {
            if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
                this.Exit();

            plane.Update(gameTime);
            lvl1.Update(gameTime);

            foreach (CommonEnemy ce in cel)
            {
                if (ce.CollidesWith(plane))
                {
                    ce.hasSpawn = false;
                }

                foreach (CommonBullet b in plane.commonBulletList)
                {
                    if (b.CollidesWith(ce))
                    {
                        ce.hasSpawn = false;
                    }
                }

                ce.Update(gameTime);
            }

            LoadCommonEnemy();

            base.Update(gameTime);
        }

        private void LoadCommonEnemy()
        {
            int randY = rand.Next(-600, -10);
            int randX = rand.Next(0, 750);

            if (cel.Count < 3)
            {
                cel.Add(new CommonEnemy(Content.Load<Texture2D>(@"Enemy/Common/commonEnemySprite"), 7, 2, "left", randX, randY));
            }

            for (int i = 0; i < cel.Count; i++)
            {
                if (!cel[i].hasSpawn)
                {
                    cel.RemoveAt(i);
                    i--;
                }
            }
        }

        protected override void Draw(GameTime gameTime)
        {
            GraphicsDevice.Clear(Color.Black);

            spriteBatch.Begin();

            lvl1.Draw(spriteBatch);
            plane.Draw(spriteBatch);

            foreach (CommonEnemy ce in cel)
            {
                ce.Draw(spriteBatch);
            }

            spriteBatch.End();

            base.Draw(gameTime);
        }

I wish to load my players, enemies, all in Level1 class. However, when I move my player & enemy code into the Level1 class, the gameTime returns null. Here is my Level1 class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Media;
using Microsoft.Xna.Framework.Input;
using SpaceShooter_Beta.Animation.PlayerCollection;
using SpaceShooter_Beta.Animation.EnemyCollection.Common;

namespace SpaceShooter_Beta.Levels
{
    public class Level1
    {
        public Texture2D bgTexture1, bgTexture2;
        public Vector2 bgPos1, bgPos2;
        public float speed = 5f;
        Player plane;

        public Level1(Texture2D texture1, Texture2D texture2, Vector2 pos1, Vector2 pos2)
        {
            this.bgTexture1 = texture1;
            this.bgTexture2 = texture2;
            this.bgPos1 = pos1;
            this.bgPos2 = pos2;
        }

        public void LoadContent(ContentManager cm)
        {
            plane = new Player(cm.Load<Texture2D>(@"Player/playerSprite"), 6, 8);
            plane.animation = "down";
            plane.pos = new Vector2(400, 500);
            plane.fps = 15;

            Global.currentPos = plane.pos;
        }

        public void Draw(SpriteBatch sb)
        {
            sb.Draw(bgTexture1, bgPos1, Color.White);
            sb.Draw(bgTexture2, bgPos2, Color.White);

            plane.Draw(sb);
        }

        public void Update(GameTime gt)
        {
            bgPos1.Y += speed; bgPos2.Y += speed;

            if (bgPos1.Y >= 600)
            {
                bgPos1.Y = -600;
            }

            if (bgPos2.Y >= 600)
            {
                bgPos2.Y = -600;
            }

            plane.Update(gt);
        }
    }
}

Of course when I did this, I delete all my player's code in the main Game class. All of that works fine (no errors) except that the game cannot start. The debugger says that plane.Update(gt); in Level 1 class has null GameTime, same thing with the Draw method in the Level class.

Please help, I appreciate for the time.

[EDIT] I know that using switch in the main class can be a solution. But I prefer a cleaner solution than that, since using switch still means I need to load all the assets through the main class, the code will be A LOT later on for each levels