True story: I was animating a design that involved multiple "filmstrips" of HD video: 6 or 8 of them with a couple dozen HD clips each. I worked on it until past midnight for an early morning deadline only to realize it would never render in time; it wanted over 2 days to process all that 1080 footage. Then I remembered that I could set up a series of proxies and render those in a giant cascade. When I awoke the following morning everything was fine. Here's how.
After Effects has an under-utilized ability to render Proxies. Proxy files are at the center of Flame/Inferno systems but a virtual afterthought in this application, where they must be set up fairly deliberately. But the payoff is that renders that might take hours or even days will complete in a fraction of the time.
There are two basic uses for proxies. By default, choosing a comp in the Project window, right-clicking and choosing Create Proxy > Movie renders at Draft quality. Once the render is completed, a toggle appears next to the comp; the point is to speedily generate a preview version of a pre-comp that was requiring a lot of cycles to view.
But it's also possible to render Best quality proxies and use them in a final render. This is useful not only to render a comp made up of hundreds of HD clips, but whenever there's a whole section of a shot that's done - say, a greenscreen key. If you've nailed the key, why keep re-rendering it every time you go to a new frame?
Instead, make a pre-comp that will become a rendered layer. You can right click to Create Proxy > Movie and switch to Best Settings, or you can make the settings you like in the Render Queue and then twirl down Output Module and choose Post-Render Action: Set Proxy.
That will speed up your previews, but by default any renders will ignore proxies unless you go to Render Settings and change Proxy Use from the default Use No Proxies to one of the alternatives. Make a new Template to reapply this to multiple comps.
You can even render a series of comps in which one render item uses a proxy from the previous, which is how I completed a 2 day render in a few short overnight hours.