Which M&P15T, there is the troy model and the current model with S&W decided do a ton of cost cutting measures to make it pretty cheap, which I really am not a big fan of.
From what I know
They Ditched the chrome lined barrels
They Ditched the Troy battle sights for cheapo magpul plastic sights
Started making their rails inhouse instead of troy battle rails
Don't think they are still using LMT semi BCG, they might be making those inhouse as well.