It seems like your runs at the moment are all just flat chat. If you really start upping your distances, this is a very good way to get injured. The idea of the long run is not to make you faster, it's aimed at making you used to spending long periods of time on your feet. The first rule of training for a marathon is don't get injured. Playing on Sunday does make things harder, but I think it's still possible.

As a guide, my GF is currently training for the Sydney marathon. She's aiming for sub 4 hours (although I think 3:50 is more likely). According to the Jack Daniels running formula, the "easy pace" for long runs should be about 5:55 - 6:15min/km, significantly slower than the 5:41min/km required for a 4 hour marathon, and a great deal slower than the 5 min/km she did in her last half. All of your runs should have a clear goal - you don't get faster in your long runs.