You have not given enough info for a guess:  More info like:  Sex, Age, how long have you been running, ave MPW when not in a marathon cycle, MPW in your cycle.  A good start is to go to the McMillan Running Calculator and put in a race time from a race not to long ago (the longer the race the better but it will take a 5K)and it will tell you all the info you requested.  The calculator is guessing you are well trained and has been fairly close for me.  Just type Mcmillan Running Calculator in gogle. Good luck

This is a point that can be confusing.  Since you have not run structured workouts like hills and tempo runs I would be conservative on the long runs as those added workouts add stress to your overall training load and you don't want to end up over trained or injured.  The main goal of the long runs is to teach your body to burn fat and get use to running for longer periods of time, do not worry about speed, the tempo runs and hills will help you with that. You should not be running your long runs as fast as you intend to run the marathon, this is a common mistake.  Usually 1 min+ slower/mile or so of goal race pace.  Running faster than this will leave you depleted as you get closer to race day, especially since you are running those other workouts. 

Hope that helps...

Unfortunately, there is no simple answer to your question.  How do you improve?  Put in the miles; do interval, tempo, hill workouts; slowly improve your pace.  Long run pace has become a little controversial.  Tradition is to run 45 seconds or more slower than your anticipated marathon pace (9:44 for a 4:15).  So 9:46 would seem a bit fast - but 12 miles isn't 20, as I'm sure you know.  One way to get a better idea of what you should shoot for is to put your target time in the calculator as the current time.  Then compare the paces given to your current (and future) workouts.

Len

As Jasko stated running your last third of your LR at or below MP will help but this should not be done every week.  Every third or so is good.

The Yassos are okay if done correct, 10 with easy jog of the same amount of time between intervals!  It also requires a set amount of MPW.  20 miles @ 9:45 pace would be 3:15 so you were 6 mins under MP which is not bad.  The last 10K can be a tuff 6.2 if you go out to fast, but I think you will be right about your goal.  Can you run a time trail 10K, that would help with a pace calculator.  Good luck