Preheated oven temp 450, forgot to lower temp for 1/2 hour when turkey inserted into oven. Do I cook this 8 lb bird for 15 minutes per pound or less

Hi Cindy, this will be fine! Do you have a meat thermometer or instant-read thermometer? The most important thing is that the internal temperature in the thickest part of the thigh gets up to 165F. If you don't have a thermometer, you'll want to cut into the space where the thigh meets the rest of the body and make sure the juices are running clear and the meat looks firm and cooked, not raw or pink still. You'll just want to check a bit earlier than you would have otherwise.