Two things jump out at me right away in your message:

• You're running approximately 25-30 miles per week. That sort of mileage will likely not support a 3:15 marathon. You should spend some time trying to build up your base and increase your mileage. Since you already had a serious overuse injury, you'll want to be very careful upping the mileage. A good intermediate goal might be to take three months to increase your mileage to average 40 miles per week. You'll have to figure out the best way for you to do that, though -- don't rush into it.

• You're running your everyday runs only a little faster than race pace for a 3:15 marathon. This is too fast! Most of your runs should be at a very easy pace. This will also help prevent injury. I recently ran a 3:11 marathon, running the last several miles at about a 7:15 min/mile pace, and when I was training for that marathon, my long runs were at about an 8:30 pace (and some recovery runs were as slow as a 9:00 pace).

The basic formula for marathon improvement in my experience is pretty easy: Run more miles. Mostly easy. Some fast. Once you get the base built up, you will want to add things like temp runs, marathon pace runs, and some tune-up races of 10K to half-marathon to work on your endurance at faster paces. Of course, a lot of factors go into a successful marathon, so you'll also want to think carefully about race pacing and fueling strategy.

My first marathon was a 4:15. My second was 3:18, my third was 3:30 (went out way too fast and crashed), and my fourth was 3:11, so I know from experience that you can improve as much as you'd like to -- it just takes time! Don't rush it; you have many years of marathoning ahead of you.

TK1980,

You have an unrealistic goal. Take Werdnam's advice regarding the running, and seek medical attention for the "Post Marathon Effects".

TK1980,

Your goal is unrealistic because you have not built a solid base of running. You have pushed your body too hard, injured yourself, and are likely to do so again given your present training and expectations. It is good that you enjoy the sport and continue running. Build a solid base. If you have only been training one year, run two marathons, and other races, broken your leg, get sick after every race, you are doing too much. I understand the mind is willing, but you have got to let the body catch up.

I suggest doing a lot of reading on runnersworld.com. They have a lot of good running articles and free training plans. 

Regarding your question about "making up" the extra 1:15 per mile: Race pace and training pace are very different things. I know it sounds hard to believe that you can run significantly faster than you usually do for more than 26 miles on race day, but that's what the training does for you. In my training for that marathon, I did occasionally run at or below goal marathon pace (with the longest being a 14 mile long run at marathon goal pace), but rarely more than 10% of my weekly miles were that fast. You just have to trust the training.

In fact, I guarantee you that if you build up to a higher average weekly mileage, run two or three long runs of 18+ miles, have a good three-week taper, and fuel and pace yourself appropriately during the marathon -- with NO speedwork and no running faster than 8:00/mile -- you can set a PR in the marathon.

Do some reading on appropriate training paces: Jack Daniels and Pete Pfitzinger have some good books out there that cover this topic.