While practice is the best remedy, I would recommend against slowing your swing down more then 5-10%. Slowing it down more than that will make your body feel out of time and will probably just lead to bad timing regarding other parts of your swing.
Instead, don't swing as hard (just a little bit less force makes a big difference), and if you're still slicing, try closing the club face slightly. To do this, hold the club like you usually do, and spin it in your hands (don't just twist the club, actually spin the grip in your hands) a slight amount to the left, so the club face is pointing towards the left edge of the fairway instead of exactly where you want to hit the ball. This is a workaround, not a true fix. This will set it up so that when you don't close the club face by the time you reach the ball (which is your problem), your club face will actually end up straight. This doesn't fix your problem, it only plays into your problem to achieve better results. Adjust how closed the club face is based on the results you see (if your slice is diminished, but still there, close it a little more...if you hook the ball into your buddy standing behind you, try opening it up a little bit).
The other thing you can do is to move the ball up some in your stance. Most beginners try to hit every ball in the center of their stance. Moving it more towards your front foot will give the club face longer to close, minimizing the slice. Note that if you go too extreme (don't make yourself REACH for the ball when addressing it, don't have it so far out on your front foot that you hit it on the toe of the club), you'll slice just as bad, so practice adjusting the location in your stance until you get a spot that works best for you and feels comfortable.
A driving range bucket of balls can allow you to focus these two workarounds, and it'll only take you 1 hour total. You won't be Arnold Palmer, but you should be able to learn how to adjust your body and approach slightly throughout a game depending on the results you're seeing. Some days, you'll have more slices than an Orange Julius, so you'll move the ball further forward and close the face more than usual. Other days, you'll have a fairway seeking ball, so you won't have to mess with a thing. Just remember, most importantly, stop swinging so damn hard. I guarantee it'll help. The driver will hit it a really long way, even if your grandmother swings it. Trust the club.