There is no lawsuit. There is not a recall on the 2015s for this issue, either, to my knowledge. Only one listed on official sites is airbag related.
It's a known issue, but what you have to realize is there are literally hundreds of thousands of Titans out there which have not had this issue, and only a relative few which have. Sucks to be in your shoes, but if your truck is in good shape and worth dropping a few thousand into, replace your radiator, flush the motor to get the trans fluid out, and do the bypass/aux cooler while you're in there, and buy a rebuilt transmission (online sources show them for $2500-ish) or have a local reliable transmission shop rebuild yours. If your motor has fewer than 150k on it, you might get another 150k out of it with a new trans.
and its a big deal on Toyota trucks and rwd suvs. that is the number one thing all the Toyota forums told me when i was looking at Toyotas last year. it seems like they all get their radiators from the same place, Toyota, Nissan, probably honda, too.