Can I temporarily replace an object with a "placeholder" to help with multiple high-detail objects? I have an object with a great many polys, so many it causes significant slowdown in the viewport.

I need to arrange several of these objects for my final render, but this would be awkward, given how slow they make my computer.

Is there a way to temporarily de-polyify the objects, or replace them with a low-detail object (with roughly the same size and shape), so that I can arrange the low-poly objects, then easily switch them out for the high-poly objects?
Select your high poly object
Go to Object Properties panel
Under display tabs, look for "Maximum Draw type"
Choose "Bounds" in the selection drop down.


Now your high poly mesh will be displayed as a simple box in the viewport.



Alternative Method

Or you could add a decimate modifier on the high poly object which would let you pull down the mesh count considerably. When you have finished positioning all the mesh all you need to do is to remove the modifier so the high poly object is restored.