Yes I agree with Nicola - it is long, but with 2 intervals there are plenty of breaks.
I've been at the theatre all week, so I've seen the show through 5 or 6 times, and I still find it hilarious and am going to see it as audience as well. I highly recommend you go and see it! the cast have great comic timing, but at the same time there are some darker and 'reflective' bits, and it is meant to be a representation of British life today (exaggerated of course).
Jez Butterworth is a genious imo (and very nice)

Oh and from what I've heard, they're not planning on cutting much after the previews, Jez and Ian (director) were pretty adamant on keeping the content (and I agree with this).