Too high of oil prices are bad just as are too low of prices. The lay offs have already started and many small oil field service companies have shut down already. Once the US oil industry is hurt enough, saudi arabia will reduce production and prices will sky rocket past where they were since we will then suffer the loss of production from defunct companies.
6.7L is a great engine. I have a 2011 with 80K miles on it and never a problem, just routine maintenance. I really haven't paid any attention to what changes there are for 2015 so i would check that out if a new Super Duty is in your future. I'd buy this truck again.