How deep is the HL15 (including the power cord plugged in)

Case looks to be about 20in (50cm) front to back.
You would need about another 2in (5cm) clearance for the power cable and ethernet cables to stick out.
However, if you get the rails, those seem to have a min depth of 27in (~68cm)

if you buy a right angle power plug you might be able to fit it in smaller than the 22in

edit: similar post about this here: Will it fit my rack? Trying to figure out before purchases