MCAT2015 will be longer. It will take you about five hours and 10 minutes to complete the current version of the MCAT. The revised MCAT will take around seven hours to finish. Yes, it will take longer to sit through it because instead of only three sections as in the current MCAT, there will be four sections in MCAT2015. Additionally, each section is expected to be longer.
MCAT2015 will be broader but at the same time, it will be more in-depth in its approach to measuring your grasp of the sciences. Keep in mind that in real life, the boundary between sciences is artificial. A molecule does not know if it is a matter of physics, chemistry or biology. You were trained to put that molecule into a box depending on the course code. MCAT2015 blurs the boundary. After all, the molecule is physics, is chemistry, can be biology, and may have psychological or sociological implications.
Thus MCAT2015 cuts across scientific disciplines (Physics, Organic Chemistry, Inorganic Chemistry, Biochemistry, and Biology) which interact in living or biological systems. There is also a section which seeks to test your grasp of the interplay between Psychology, Sociology and Biology with the context being basic research methods.