Also, while you can certainly experiment with large textures first, to see what kind of change they make, keep this in mind for ALL optimization, memory, speed, whatever.
DO NOT OPTIMIZE CODE JUST BECAUSE… If you don’t have a problem, DO NOT OPTIMIZE!
If you DO have a problem, always start by using the profiler:
Window → Analysis → Profiler
Failure to use the profiler means you’re just guessing, making a mess of your code for no good reason.