GRB 100615A SEDs at three different epochs: GROND grizJHK upper limits taken 24 min after the trigger (upper panels) and Gemini-North K and Ks upper limits taken 5.5 h and 9.2 days after the trigger, respectively (middle and lower panels), with β_OX fixed at β_X − 0.5 and the optical suppression modeled with the MW or starburst extinction curves. Black dotted line represents the best-fit value for the X-ray spectral slope (β_X = 1.35). Dashed red lines enclose the 90% uncertainty in β_OX.