I haven't played for while but BLs is at heart a CO-OP fps. It's quest/mission based. So you pick up one or more missions and go out with your coop partners and shoot anything you can find. The key is not to let your co-op partner die. So when they go down you get over to them and revive them before the respawn timer runs out. If you don't get revived, you respawn (at an ingame $ cost) at the nearest genetic sequencer unit (or whatever they're called ) And you go from there and get back in the fight. If you can't complete a mission in the time you have (you mention 15mins at a time) then you will have to start it again next time you play. You can play alone but it's best played in coop.