OK, I read it more carefully and see that you are doing 4 x 200m at 32, 32, 28, 28 and are walking ~5 min in between. That is closer to what I was thinking. A few yrs ago I read a great article by that 50 year old American that broke 15:00 (he is also a coach I guess) about a basic speed workout that he does and has his runners do. I think it was on Runner's World.com?
Anyway, it seemed very smart and centered around building up to top speed over 50m and then doing different things to develop your speed.
I don't think you need such a fancy approach, because you are 27, but it might be worth a look. I could not find the article but his name is Pete Magill and there seem to be plenty of articles on Plyos and sprints on there.
One thing we did was just do fast strides on the grass playing field. We did not time them and they were usually 100-120m on the soccer field. We would sometimes do as few as 8 and in XC we did them slower and did 24.
In any case, I would heed what others have said and focus on running 20-30 minutes a day (alternating a hard-easy plan) and doing strides on grass for the first 3 months. Like this ...
M: 20 min easy + strides (6-10)
T: 30 min easy
W: 20 min easy
T: 30 min easy
F: 20 min easy + strides (6-10)
S: OFF or other sport
Su: 30 min easy
This would be 20-25 mpw.
You have good speed already if you can run a legit 27 and 28 in the same WO.
Start by increasing your Sun run by 5 min every two weeks and then increase your 30min runs by 5 min a month. Once you reach :45 and :40 start by increasing your 20 min days. If you push the pace, do it on hte longer days. Looking like this ...
M: 30 min easy + strides (8-10)
T: 40 min moderate
W: 30 min easy
T: 40 min mod
F: 30 min easy + strides (8-10)
S: OFF or other sport
Su: 45 min mod
This is just 30-35 a week.