Very long. If you hadn't seen the films I'd say definately read them though because they are brilliant. I grew up on them and thought they were the best thing since sliced bread. Now though, i can't get back into them and there are faster, more engaging books out there. Thry Scott Lynch "Lies of Locke Lamora", Joe Abercrombie "First Law" or any Drenai books by David Gemmell instead (Waylander and Druss books are my personal favourites but "Quest for Lost Heroes" is an excellent stand alone)
I would definitely read them. I saw the first film before reading any of the books and it inspired me to read the Hobbit and LOTR trilogy before the release of the Two Towers. It was well worth the time and effort. The films were fantastic, but the books are so much more; they will add depth to the films and you will see Middle Earth from a different perpective. Enough from me; get reading!
honestly, i have never read them either, though the children of hurin and The Silmarillion are among the best books i have ever read, having the same problem with the trilogy though since i have seen the films but i think the silmariooions would give you all the background on middle earth you would need and the children of hurin expand areas not shown in the trilogy. just my opinion.
BUT its still the second best selling novel of all time, only beaten by Dicken's A Tale of Two Cities (which has been around 100 yrs longer) so thankfully you are in the minority with your opinion. The Lord of the Rings is hard to read, there are easier,(and if you prefer easier,therefore more enjoyable) and better written novels out there. BUT its a true classic, full of great characters, amazing descriptions (especially landscapes/places) exciting battles and adventure and the detail of the world is 2nd to none. Each to their own but it will always be Number 1 for me.