I am a young cook, and tonight I am home alone and was fairly hungry. I decided to poke about in our cupboard and fridge. I cut some potatoes into slices, minced some onions, and cut a few white mushrooms. I mixed them together and added a few peas and some sliced carrots. I then seasoned them with thyme, sea salt, and black pepper. I currently have them in the oven at 400 degrees Fahrenheit, and they have been in there for about fifteen minutes. How much longer should i cook them, and should I change the current temperature? Thanks.