The Apple Logo Is Pictured Inside The Newly Opened Omotesando Apple Store At A Shopping District In Tokyo
Check out the cool and useful features of the new Apple iOS 9. Pictured above: The Apple logo is pictured inside the newly opened Omotesando Apple store at a shopping district in Tokyo June 26, 2014. Reuters/Yuya Shino

Apple Inc stock is expected to surge higher in 2015 as investors remain optimistic about the company's performance in the holiday quarter. Analysts believe iPhone inventory levels and holiday sales will be crucial catalysts for Apple by the end of the year.

Piper Jaffray analyst Gene Munster believes that if Apple can keep its iPhone inventory "tight" throughout the holiday quarter, there will be greater expectations for the company's sales forecasts in March. The firm currently maintains its "Buy" rating on Apple stock. Munster told CNBC that iPhone inventories in about 80 of Apple stores are currently at 50 percent which the firm sees as "really tight." The tight inventory level is expected to bring positive gross margins for Apple for the March quarter in 2015.

Munster added that the larger-screened iPhones has given Apple an edge as it is a market they haven't tapped in the past. The analyst said the sustainability of the iPhone's cycle will go beyond the March quarter and into the June quarter.

The record-breaking launce of the iPhone 6 and iPhone 6 Plus has reflected in Apple sales around the world despite initial problems of stock shortage due to a surprisingly high market demand the company did not expect. According to previous reports, Apple sold more than 10 million units of its new and bigger iPhones during their first opening weekend sale following the launch.

Apple stock has soared 45 percent to date but 2015 is expected to be crucial to the company's shareholders. According to Motley Fool, Apple's earnings for the September quarter had surpassed expectations with earlier guidance for the holiday quarter also predicted to be record-breaking. The surge in Apple stock is buoyed by the success of the iPhone 6 and 6 plus with the iPhone category representing more than 63 percent of Apple's revenues.

Analysts believe the healthy demand for the iPhone 6 and iPhone 6 Plus has been the main growth driver of Apple's success for this year and its quest to be a trillion-dollar company based on market capitalisation. In 2015, investors can evaluate how Apple Pay, the company's mobile payments system, and the upcoming release of the Apple Watch can affect the Apple stock.