There aren't any magic workouts, but if you're already at a high level of general fitness, these two should give you a good bit of stimulus at race pace or slightly faster without being too taxing.
Workout 1:
12-20 min. warmup jog
Some light dynamic drills (if you've been doing them all pre-season) to help warm up a little more (these also help with running economy if they're done for months)
4-6 short (10-15 secs.) buildups (each one a little faster than the previous)
4 x 200 starting about 4 secs. slower than 1,500 goal pace and cutting each one down by about 2 secs. so the last one is about 2 secs. faster than goal pace, with 60-90 secs. between reps (the first 2-3 reps are still part of the warmup process, also helping to establish pace familiarity for the bulk of the workout to come, with the last rep or two starting to segue into a real effort as part of the workout proper)
3 min. break after the last rep
3 x 600 starting at current 1,500 pace and cutting each one down by 2-3 secs. so the last rep is 2-4 secs. faster than race pace, with 2:30 rest after each rep (if you're at 4:00 for 1,500, the 600s would be run in 1:38, 1:35-1:36, 1:32-1:34; you can use less rest if this is too easy, but it isn't necessary, as this isn't supposed to be killer workout or an indicator workout, just a decent stimulus at race pace or a little faster)
Follow the last 2:30 rest period with 4 x 200 cut-downs in a similar fashion to the beginning set of 200s, with the last rep blowing the pipes out a little more if you feel good
15 min. cool-down jog
Light stretching
Workout 2:
12-20 min. warmup jog
Light dynamic drills
6-8 short buildups (a couple of extra ones this time since you're not doing any 200 cut-downs before the main part of the workout)
3 sets of (3 x 400 / 1 min. walk/jog between reps) / 3 min. walk/jog between sets (do the first set at current 1,500 pace or maybe a second faster (the 4:00 guy would run 63-64), then run each successive set about one second faster than the previous set; this isn't an indicator workout either, since if it was all-out, you could probably run all 9 reps right at 1,500 pace using only equal rest-to-run periods (about a minute) without taking 3 min. between sets, but (like Workout 1) it isn't supposed to be a 100% all-out, balls-to-the-wall effort)
15 min. cool-down jog
Light stretching
Again, these aren't the hardest possible workouts. But workouts should only rarely be the kind that are harder than the races themselves (and they sure can be). You normally want to be really fit in general terms, then just touch on your race pace or goal pace enough to finish the workout strongly and recover enough to feel fresh within 2-3 days before you add another stimulus (this doesn't have to be the same stimulus; it might be a tempo effort or some short speed work or something else different than race pace, or it might be a race). In any event, you don't want race pace to feel incredibly labored as a result of overdoing a single workout or from repeating these race-pace workouts too frequently. Unless it's done in lieu of a race (in the middle of a 2-3 week period with no races), a race-pace workout should usually be pretty challenging but not so tough that you can't believe you actually finished it.