Nah there's no benefit, just upgrade straight to 3.15
How do YOU know, eh? There is always some benefit in something to someone and if anything we've learned the hard way (with PSP) that the lower the FW the more chance and earlier you might be able to install CFW and vice versa. It's simple - lower FW = usaully more holes in it. So if that's you goal - stay low. If you don't really care about CFW - then it's up to you
If you want to really want to JB then you might as well but if you don't it is unknown as whether the JB will be made to work with 2.76 (Probably will but will probably take time) and as GrandpaHomer has said the lower the better if you want CFW if your not bothered then you might aswell upgrade.