With 13 weeks to go, changing plans to another one aimed at your current running ability (but perhaps a little more intensive) would be no problem. But there really is no need to panic. You could also choose to stick with the current plan, but throw in an extra run for as many of the remaining weeks as possible... even if it's a 3-6 mile recovery pace run, it will make a big difference. It's that latter route that I'd recommend... but if you can also "lose those pounds" at a steady, sustainable weight, then that will make a great difference too.
But you are just having a crisis of confidence (common, but in your case, unnecessary)... because the times you're running are great. Surely you can see that a 2:22 half marathon, 15 weeks from race day, shows great promise. And 2:38 in a half that includes 6 miles on a sandy beach... likewise.
No personal experience, but it makes sense. Depression can be sapping and the best races need physical and psychological powers to combine... so maybe that puts you at a disadvantage.
Hopefully someone with direct experience will share it with you, but one question would be whether your weight has changed since last year. Depression is quite often accompanied by a weight change (up or down)... but if you've put on 10 or more pounds since last year, then that could explain the entire difference.