I have heard that if you run 2x[400 (45 sec rest), 800 (90 sec rest), 300] with 3 minutes between sets, the average overall time of the two sets is indicative of 1500m performance.
ex: if you run (60, 2:01, 44) (59, 2:01, 45) You will be in ~3:45 1500 shape.
Might as well just race a 1500 at that point. Doing 2 x 800 at that pace with so little rest is hard enough.
If you want to know your 1500 shape...
race a 1500.
Predictor workouts are stupid, use workouts build fitness and to prepare yourself for the stresses of a race and then go and race.