The only reason they should be ranked at all is because this is one of the worst years in ncaa football of all time (very, very few good teams this year). LSU has played two good teams this year and got flat out dominated by both. Defense is their strong area and they gave up over 50 to the only two great teams in the sec. SEC is very overrated this year. LSU is not a good team, yet still might be the third best it the conf. I think they are better than Alabama.
With all that said, who would you put ahead of them in the rankings? LSU may not be good, and yes 15 seems VERY high for them, but who behind them is better? Only teams behind them that I would take at a pk line vs them on a neutral field is Oregon and BYU. A team like Ball State would lose to LSU by 24+, yet is ranked 18. College football is just flat out terrible this year. If you look at the rankings it's a bunch of bad teams with some very good ones at the top (minus bama and tech, still think they are frauds). I mean I still can't believe teams like Ball St, and Tulsa are ranked. Hell, even Minnesota isn't a good team but at least they are beating BCS teams. Ball St has beaten one BCS team and that is IU, and they are one of the worst there is. Tulsa's biggest win is against who, Rice? New Mexico? Ridiculous that these teams are ranked.
Yes LSU is overrated, but no they really shouldn't be ranked lower. Just a sad year for college football fans.