That's exactly what I've done. For best results run slower than you would on your 10k pace (if you know yours already) it's up to you how far really I would say 15k is fine.
I do....slow run monday, hard training on Wednesdays (I'm part of a very nice local running club) slow run Friday and a nice slow long run Sunday. I've found this very good for me so far and I'm improving my 10k time each race!!
Benefits of the running club are the people your around, as they enjoy what I do etc.