Adding a third running session will help for sure. There's lots of ways to get quicker really.
If you are already running your 2 training runs pretty hard (I get that impression from your reply) I would suggest the 3rd session could be a longer slower session. As you don't want all your runs to be at high intensity otherwise you may get injured. Especially if your doing other intense training during a week.
Alternatively you could change one of your current runs to a slower longer run with your running buddy (say 12-14k?). Then you could do an interval session to work on your speed, so short bursts (2mins) at about 3-5k pace followed by a slow jog recovery for the same time.
Just consistently running 3 times a week will help you improve either way. I'd just be careful of adding intensity and distance at the same time.