Unfortunately, there’s not enough room to mount a 120mm fan on the rear. I guess the answer to your question then is technically no? I haven’t measured, but I think you could get a 80mm fan ( or two side by side) to mount there. Either way, you won’t have room for any fans if you go with the rear SSD mount.
You may have seen the post below on a larger 5U version of the HL15 referred to as the “Beast”. It’s possible the chassis might support a 120mm rear exhaust fan.