We report on the demonstration of an ultra-highsensitivity superconducting hot-electron-bolometer (HEB) heterodyne receiver at 2.5 THz with a low-power-consumption quantum cascade laser (QCL) as its local oscillator (LO). The 2.5-THz QCL, with an electrical power dissipation of about 0.9 W in continuous wave mode, is integrated with a spiral-antenna-coupled niobium nitride HEB mixer in a single block. The mixer performance is barely affected by heat dissipation from the QCL when the receiver is cryogenically cooled either by a wet LHe Dewar or by a closed-cycle 4-K pulse-tube cooler. Measured with a vacuum setup, the heterodyne receiver exhibits a double sideband receiver noise temperature of 800 K at 2.5 THz with the IR filte contribution corrected, which is approximately 7h upsilon/k(B). And the Allan variance time at 80-MHz noise bandwidth is found to be about 10 s when a proportional-integral-derivative controller is adopted to control the LO power.