Colour-composite images of HCG15. The optical RGB image is constructed using i-, r-, and g-bands from Data Release 2 of Dark Energy Survey (DES). Green colour and contours (top-right) denote our XMM-Newton X-ray data in the 0.7 − 2.0 keV range, smoothed with a Gaussian of 7 pixels (14 arcsec) FWHM. Radio data from ASKAP at 943 MHz (lower-left) and MeerKAT at 2.4 GHz (lower-right) are shown, with red colour and contours denoting continuum emission and blue colour denoting linearly-polarised emission. All radio data are shown at a 20 arcsec resolution, as indicated by the hatched circle in the lower-left corner. Contours start at 3σ and scale by a factor of $\sqrt{2}$. Cyan vectors denote the orientation of the magnetic field, with vector size proportional to the fractional polarisation. Yellow circles and labels identify the six group-member galaxies; cyan ‘+’ sign in the top-right panel denotes the SZ position of a background cluster at z ≃ 0.88 reported by Klein et al. (2024), with the circle tracing a 500 kpc radius.