The suit seeks in excessive of $5 million in damages, and the complaint goes on to accuse Apple of advertising all sorts of performance and security upgrades, among other great features, despite internal tests showing iOS 9 hurt iPhone 4S users more than it helped. Furthermore, the lawsuit attacks Apple for foisting updates on users, who are more inclined to buy new Apple devices when their tech goes awry, as users won't want to lose apps and other data that live in Apple's ecosystem.
And as Apple Insider points out, this isn't the first lawsuit against Apple of this nature, though a 2011 suit by iPhone 3G users pissed about iOS 4 was thrown out in court after a year.
No date has been set for court proceedings. So for now, the best response to your iPhone problems is ¯\_(ツ)_/¯.