I have a list of entities which implement an ICollidable interface. This interface is used to resolve collisions between entities. My entities are thus:

• Players
• Enemies
• Projectiles
• Items
• Tiles

On each game update (about 60 t/s), I am clearing the list and adding the current entities based on the game state. I am accomplishing this via:

collidableEntities.Clear();
collidableEntities.AddRange(players);
collidableEntities.AddRange(enemies);
collidableEntities.AddRange(projectiles);
collidableEntities.AddRange(items);
collidableEntities.AddRange(camera.VisibleTiles);

Everything works fine until I add the visible tiles to the list. The first ~1-2 seconds of running the game loop causes a visible hiccup that delays drawing (so I can see a jitter in the rendering). I can literally remove/add the line that adds the tiles and see the jitter occur and not occur, so I have narrowed it down to that line.

My question is, why? The list of VisibleTiles is about 450-500 tiles, so it's really not that much data. Each tile contains a Texture2D (image) and a Vector2 (position) to determine what is rendered and where. I'm going to keep looking, but from the top of my head, I can't understand why only the first 1-2 seconds hiccups but is then smooth from there on out.

Any advice is appreciated.