From my experience, you have to build up both mileage and quality to go sub 2:45. But I'm not convinced that the speedwork needs to be structured - ie, track based. Introducing tempo segements into medium- to long runs is a good way of combining mileage and quality.
For slower target times - eg, sub 3 hours - I don't think that speedwork is that important at all. I'm always surprised that the RW schedules, for example, recommend speedwork for people trying to run 3:30 (and slower). I am convinced that better advice would be just to get out and run a bit more.
The problem with only two runs a week is that you are not doing enough training to provide basic fitness conditioning.
Without that foundation, there is a risk that introducing speedwork will result in injury.
Also, you say that your 10k time is 62 minutes, and your normal training session is an hour on the treadmill. What sort of pace are you running the treadmill at: 8 or 9kph? In any event, I don't suppose you could really call it a quality session. You probably would be better off trying to run 3 times a week, for 40 minutes each, but working to get the pace up above 10kph for all of your runs.