We present low resolution interstellar spectra of the Ca Ii K and Na I D lines towards 12 stars in the M 15 globular cluster. These sightlines are used to study the small scale structure of the interstellar medium, over scales of a few arcseconds to a few arcminutes. A high-velocity cloud is detected in the Ca Ii and Na I lines at a LSR velocity of approximately ~ 70 km s(-1) . Tentative velocity and equivalent width variations are observed on scales of a few arcseconds; however, higher resolution data are necessary to quantify the magnitude of these variations. We discuss these observations and their importance for future studies of this high velocity gas at high spectral resolution.