iMovie taking very long time

I have 2 computers: a Macbook Air and a Mac Mini at work. I routinely use my Macbook Air with iMovie. Recently I've begun using the Mini at the office. It seems that any iMovie work done on the Mac Mini takes much longer than it does on the Macbook Air.

I would have assumed that the Mini would be more powerful. It is a 2011, Intel cor i5, with 4 gig of Ram. That's much better than the Macbook Air specs.

Any thoughts on why this might be happening?

Thanks