"Relaxed" is pretty vague. If you're doing these at 3k/5k pace with a truly full recovery, then this is no problem. You improve economy at race pace by running race pace, you accumulate almost zero oxygen debt, but you still rev up your aerobic system a bit. I would recover for at least equal distance of just jogging, or if you want to run faster during the recovery, then take even longer between reps. This would be an easier session than some of the faster alactic stuff that others have proposed. Distance runners never respect how much strain a true sprint workout can place on your nervous system.
If you're running any faster, then you're going to be working on speed endurance, and this is a real workout.