so this is what I am thinking

300 legg quaters
6 gallon of dirty rice
6 gallon of slaw

first is this a complete meal
second ar ethe quainties semi correct
thanks in advance

Yes, they will be big eaters, but still, this is a LOT of food for 150. Here are some thoughts

300 leg quarters- no more than 140 pounds- cut apart about 1/3 after cooking, so people can take a quarter and a piece.
6 gallons of dirty rice- OK, maybe some left
6 gallons of slaw- 5 plenty

You have a menu problem here. In 150 people, there may be some vegetarians, and with the meaty dirty rice, there is nothing for them to eat. A quick solve would be to do a meatless rice, such as an almond pilaf, and a side dish of meatless beans, about 4-5 gallons, could be a vegetarian baked bean or white bean casserole with corn, or some such. This would also make sure everyone has plenty of food.

12 gallon of tea about right, probably none left.