Out of memory! UnityEditorInternal (Dragging Prefab)

On dragging and dropping a prefab on to the scene view, I get this error. I am using a Macbook Pro with 16gb of RAM so it really shouldn't be running out of ram. The prefab contains a 2D map for my game (featuring 2 x 128x128 Tile Maps, some NPC's and some colliders). I can understand it needing quite a lot of memory but with 16gb of memory to play with in the IDE it should be able to cope? Coming from a flash builder background - there was a way I could assign more memory to Flash Builder to avoid memory issues, is there any way I can do something similar in Unity?