Aims. We present medium resolution ultraviolet interstellar absorption measurements recorded with the HST-COS and FUSE spectrographs towards two post-AGB stars (K 559 K 648) located within the M 15 globular cluster (l ~ 65°, b ~ –27°). By sampling interstellar gas over the 10.4 kpc sight-line towards M 15 we wish to reveal spectral features that are associated with absorption due to the foreground g1 intermediate velocity cloud (IVC), whose distance has previously been constrained to lie between 1.8–3.8 kpc. Methods. Inspection of the UV line profiles recorded towards both stars have revealed measurable IVC absorption at Vlsr ~ +61.5 ± 5 km s-1 in the profiles of the CI, CII, CII*, CIV, NI, NII, OI, OVI, AlII, SiII, SiIII, SiIV...