Why is camping a problem to you in S&D?? If your defending thats fine if you want to camp surely? Oh, and if the team attacking you want to camp well then thats up to them but ofc they will need to attack at some point else they will loose the round. I'm sure you know all this anyhow.
I personally would keep the round time as is. I always felt is was a little too quick in CoD4 but then a good team will always play to the time they have available.