I've never fed 150, but when I have to feed a crowd my go to dish is pulled pork. Buy several pork roasts, season with onion, garlic and chili powders, salt and pepper and pour root beer or cola over it and slow cook all day in a crock pot. I've fed 50 this way from two larger crockpots so you'll need to round up a few extras. When the meat is done, remove excess juices and shred with forks. Pour BBQ sauce over the top and serve on rolls or buns.
The other way I've done it is a Mexican taco bar as mentioned above. Two kinds if meat (ground beef taco meat and salsa chicken) and then all the fixings so everyone could do their own tacos, taco salad, nachos, or burrito.