M15 is a little further away from us at 33,000 light years than the center of our galaxy. It is quite large, estimated to be 175 light years wide, and to have several hundred thousand stars. M15 is one of the densest globulars, in fact astronomers believe it has experienced a core collapse. Of the 175 light year extent, half of it's mass is found within only 10 light years of the center. Because of this concentration of mass, there is some speculation that there may be a black hole at its center. There's even speculation that M15 may be the remnant core of a baby galaxy that our Milky Way absorbed very early in it's evolution.  These things invite further study, and because it resides in an area relatively clear of the obscuring debris and  gas of our galactic core, it is more easily examined and observed. Visually it is not that large, but because of its bright dense core, it can be easily seen with just binoculars. However even with large amateur telescopes the dense core is difficult to resolve.

10" F6.3 Schmidt Cassegrain Telescope, (1600mm F.L.)  Modified Canon 300D camera with a Baader coma corrector and IR-UV filter, placed at the scope's prime focus
8 photos aligned and averaged together, then brightness, color, and contrast enhanced. Click on photo above for a full frame full rez image.
Each photo, 60 seconds exposure at ISO 800