A full HASELL check is a bit of overkill for EX15. A verry good look around, especially behind is sufficient, followed by T's and P's. If in a warrior where the rearward view is restricted, then this might involve a 90 degree turn to check your six. The exercise is to teach the proper technique for executing a 180 aboutturn in a tight space (ie a valley avec low cloud). No real time to go through a full HASELL in that situation.
A HASELL check is really to check your airspace is clear if you are about to commence 'high energy' or 'unpredicable' maneouvres like stalls/spins or aerobatics.