Immigration lines have been pretty terrible recently - I know people who have waited 30 mins in fast track during peak hours.. Not sure how bad 315AM is likely to be - it's not a time when TK has arrivals, so maybe lines won't be too bad.

If lines are long, would recommend going through immigration all the way down the hall by domestic transfers, across from the Göç desk. it's a longer walk, but I've never seen a line at that desk, presumably because most people don't know it exists.