If you don’t need to move each box separately or show/hide each one separately; There’s no reason why you can’t export all of them as a single mesh and do what told up there.
If you need to move or show/hide each one separately, you should import only 1 box into the engine and work with actor instances instead.
Importing it all as a single all you have to do is add a simple box collider and set ‘Use Complex as Simple’ and their mesh will be used as colliders instead of the simple box around all of them.