Why does iMovie take so long to import a 300MB video?

Hello.

Basically I have a video file converted via Handbrake so that it would be imported into iMovie. After the conversion, I dragged the MP4 video file into the event. I got a pop-up saying that it would take three to six hours. The resolution of the clip was at 1280X720, at 300MB, it was 15 minutes long. My Mac is rather high specd with a 2.5 Ghz Quad core i7, 4GB ram, 750GB HDD etc. So it shouldn't take that long to import. Can anyone suggest why this is happening? Three to six hours is unacceptable even when they showed how smooth it was on the Keynote for this.