When you have 4000 actors (4000x 3x boxes = 12000 boxes) in wireframe, you get low framerate because the editor is swapping to disk even if RAM is available.
Either if there is a setting for editor max memory or make it use more memory to prevent SSD reads, its slow even with under-used processor and full disk bandwidth.
Are they unique objects? If you’re going to have that many objects it needs to be optimized so that things can be instanced.