Crash in Nether Fortress when near Blazes: ExitCode-805306369

Minecraft lags hard in the Nether, but is remedied with Optifine. Once I find Blazes, I can fight a few and even hang out near a spawner for up to 5 minutes, then, with no warning, the game crashes. When I re-enter my world/realm, I'll show up where I was when I crashed, but dead.