DigiTimes is reporting that Apple has started receiving components for ultrathin 15-inch MacBook Pro in limited quantity. These components will be used for test production of the new MacBook Pro with final product shipping in Q2 2012. According to DigiTimes:

Estimated by the product planning, mass shipments of the notebook device will start in March and could be cataloged in either the MacBook Air or MacBook Pro line. Apple currently has three screen sizes for the MacBook Pro - 13.3-inch, 15.6-inch and 17-inch.

While a 15-inch ultrabook model would be considered a full function machine, which consumers normally expect to have an optical drive, limitations over the thickness restriction of 0.8-inch for the ultrabook means the launch of a 15-inch machine with an optical drive and a thickness of less than 0.8-inch may not be in the plans until a later time.

It has been rumored since 2010 that Apple has been working on an ultrathin MacBook Pro model that will adopt many features of current MacBook Air like no optical drive and SSD, but offer MacBook Pro like performance in a slim and less the 5 pound package. We believe by second quarter of next year all the pieces will fall in place for Apple to ship an ultrathin 15-inch MacBook Pro with launch of next generation Intel Ivy Bride processor, cheaper SSDs and 28nm graphics chip from AMD.