Yes, sadly Raid Parties do get a drastically reduced experience gain. To compare, I am running 5 toons and getting about 17-24XP a kill right now at level 9, on mobs ranging from 7-9. It's not bad and I know it will be picking up, but sorry to hear that you are only getting about 6 XP a kill. My only suggestion would be to drop one of the gnomes sadly to make the grind easier, and then maybe pick that toon and power level it up once you reach 70.