I've done the trek back and forth between T7 and the *Alliance lounge too many times to count. My record is I think 18 minutes to do the walk. Yes you can walk outside between terminals and reclear security, and in some circumstances it might be quicker, but I prefer to just do the walk airside either direction as it removes any uncertainty about security wait times.
Use your activity app on your iWatch (if you have it) as you will definitely close your rings with that walk! :-)