You should run after pretty much every ride. Just for 15- 30 mins.

I am in kind of the same boat as you. My run performance is about the same time-wise as last year, but my bike time is MUCH better this year. The slower run times are liekly a trade off for your faster swim and ride times. If you are faster overall, I really wouldnt sweat it too much. But if you KNOW you can be faster on the run, make it a focus for the next 4 weeks. Maintain fitness on the swim and ride, and really work your runs. Taper properly for your race and you should be ok.

Remember that it usually takes 6 weeks to see significant improvements as a result of speed work. So instead focus on form. Do strides, butt kicks, high knees, and skips if you dont already do them. Build them into the end of every workout. Preferably barefott on a football field or something similar.

Good luck.

As noted above, expecting significant speed gains in 4 weeks tends to be a little unreasonable. I'd be careful about adding a big chunk of running all at once, as that tends to be an invitation to an overuse injury.

How much are you running now, and at what levels of intensity?

I hope you mean you're running 15-20 MILES a week :D

Building speed is really a long term endeavor. You can get quick and dirty results from interval work (though 4 weeks may be a little TOO quick) but I think volume is an often overlooked component of speed. That's not to say that high intensity workouts are not necessary, but I think there is a temptation to short-circuit the process of building a solid aerobic base combined with higher-intensity steady state workouts by introducing intervals too soon and too often.

I don't know that more bricks are necessarily the answer. Certainly, there are reputable folks who advocate a run after every ride. I've never been able to do that, owing to some biomechanical deficiencies, so I've had to race on no more than 3-4 days running a week (on alternate days), with weekly averages in the 30-45 mile range.

That said, I was able to turn in Olympic distance run legs in between 6:20 and 6:50 miles, and road race PRs of 36:00 for 10K and 1:00:15 for 10 miles. Granted, that was a few years ago!

Anyway, after all this beating around the bush, while I'm sure you'll hear a plethora of opinions, each of which is very important to the holder, my own is this: gradually increase your run distance (at least into the into the 25-35 mpw range), with a significant proportion in your 70-80% KHR range, a smaller proportion in the 80-85% range, and interval training added in the 6 weeks prior the taper of your big race(s) of the season.

An interesting note-when I look at the years I did my fastest races, they were always the years when I raced the most!