Hello there! I have an unusual problem with a possible solution that perhaps might show what's going on under the hood.
I'm working with multiple layered illustrator files in an AE comp. Upon initial import, the program responds nice and fast as expected. After about a minute, a switch flips somewhere, and the update rate goes down about half the original speed, then further down the more layers there are. It gets down to where the preview and render speed are near unusable.
This happens on multiple computers in the office, all running the latest AE 13.7.2 on Mac El Capitan 10.11.4. I've tried rasterizing on/off, save the illustrator files as CS6 or earlier, etc. I haven't tried separating all the layers into individual illustrator files, as I could use that feature for keeping myself organized. I also haven't tried these projects in Windows yet, I suspect it may have to do with El Capitan and it's recent RAM preview issue.
However, I may have found a clue. I can get it to come back to the original refresh rate by replacing any of the illustrator files with itself using the 'Replace Footage' command. Once done, it's like it's a brand new project and runs like a charm. This clip shows how after replacing the footage, the RAM preview just screams by, where before it was just chugging.
Then again, a switch flips again back to super-slow after about a minute. On this clip, this switch gets flipped at :13 and 1:38 (when the bounding box appears). It's a pretty instantaneous flip, no gradual slowdown here.
Anyone have any clues as to what this might be or other ways I might be able to get around it? Perhaps it's a bug?
First, make sure AE is up to date. The speed of rendering depends a lot on what's in your AE files. I tried to import an .ai file as a comp retaining layer sizes the other day that had 900 layers as a test. My monster Mac Pro just sat there doing nothing. I grouped objects into 10 layers and the file imported instantly and everything worked just fine.
Another reason for rendering and previews instantly slowing down are a lack of system resources and poorly set up preferences for memory and disk cache. I've not noticed huge slow downs but most of my comps are under 7 to 10 seconds. I tend to comp up shots that are edited in Premiere Pro rather than build 3 or 4 minutes in a single comp. Sometimes I'll nest a few short comps in a master comp for rendering to create a sequence, but that is the exception.
More details about your project and your AI file would help. Other than what I mentioned I have no idea what may be going on.
After some more testing, I'm inclined to point the finger at El Capitan. The same projects with the same software versions run just fine with no slowdown on Yosemite computers. I may need to try to downgrade to see if the problem persists.