You would have to block all the numbers in the group I think. IDK as I never used Group SMS.
Is it mandatory for your job? Or is it just some people from work on a side conversation?
If it is not official, ask the group to drop your number. Blame in on your wife/gf/mother someone else who might complain about all the notification noises.
If it is official, see if they will switch from SMS to some other App available on any platform, BBM, Skype, Whatsapp, something. Then you can shut off the sound and vibration independently through notifications + acxtions.