Facebook has warned of heavy investments in 2015 as it steps up efforts to expand a collection of products that include messaging service WhatsApp, photo-sharing service Instagram and virtual reality headset maker Oculus Rift. As a result, Facebook’s operating expenses rose 83 percent in the first quarter as R&D costs jumped 133 percent and marketing and sales spending nearly doubled. The cost rise is one thing that can derail this story,” said Macquarie Research analyst Ben Schachter.