Too Many CH Dynamic Links in AE Project File?

A proxy file is something that you're temporarily replacing your original or full resolution file with so you can work faster. Traditionally, this workflow is used for editing something like 4K or raw footage on a machine that can't handle the original files so you create lower res files to edit with and then replace those proxies with the originals during export. This is also used in After Effects in a number of ways, but in your case it would simply mean turning your Character Animator comp into a flattened video (using a format like ProRes, Cineform, or DNxHR) that will play back smoother. A checkbox will appear next to the item in the Project panel and when it's checked all instances of that comp will be referencing the proxy file, and when it's unchecked all instances will reference the original, Dynamically Linked comp. Here's some more info on that workflow: https://helpx.adobe.com/after-effects/using/footage-items.html#placeholders_and_proxies

Edit: That being said, what is the reason you're using Dynamic Link. Are you still updating these comps in Character Animator while you're compositng them in After Effects or are you finished animating them? If you're done making edits, or you're not actively updating them where you need to see a real-time change when flipping back and forth from CH to AE, you should definitely be rendering out your comps as videos via one of the many methods available to you—directly from Character Animator, by queueing to Media Encoder, or by using proxies as a means of rendering a full res file, rather than the traditional lower quality one.