No, we wouldn't need this. How we could come to figure out and understand "the brain"[1] without understanding its smaller components is worth several science classes mostly involving maths, most of which I haven't mastered and thus won't arrogantly attempt to explain. We've managed to figure out other complex systems without understanding their components in detail. For one point of comparison, we'd already had a pretty good idea of how inertia and motion worked (Newton's laws) long before we understood in detail the atoms and forces acting upon/between them.

Then there's also the problem of your estimate. 500 years is a rather exaggerated timeframe. Twenty years ago I could've had the most prominent field experts tell me humans would never in the next three hundred years figure out biology even for the simplest of living organisms, because they were simply too irreducibly complex for that. And then a few years ago we simulated an entire worm's nervous system and gave it enough of a body for it to use, move around, and receive input from its entirely-fictional environment. Now we've got people working on doing the same thing with a cat brain. We're nearing breakthroughs in creating fully-synthetic, fully-functional animal organs that you can essentially real-life drag'n'drop to replace a failing natural organ without complications.

Knowing the above, are you really sure it's not 15 rather than 500 years?

[1]. (which is about as meaningful as saying we understand "weather", which is really a huge messy amalgam of many completely unrelated things ranging from fluidic motion and thermodynamics all the way to plate tectonics and even anthropology, after a fashion)