Top panel: Large Millimetre Telescope (LMT) spectrum of J154506 obtained with the Redshift Search Receiver (RSR) instrument. Transitions with S/N > 3 compatible with either the J154506 redshift or the local molecular clouds are marked with vertical dashed lines and labelled in teal and grey, respectively. Bottom: Velocity comparison of the continuum-subtracted line profile for the ¹²CO(4-3) line detected with ACA and LMT, respectively (left), and ¹²CO(4-3) versus ¹²CO(6-5) transitions from ALMA/ACA (right). The LMT spectrum in the bottom panel is binned to two-channel width to match the velocity resolution of the compared lines.