Does this happen in the very same project if you backsave it as an AE CC 2014 project file?
Or is this just more AE CC 2015 Weirdness?
What is the exact message that you're getting?
I doubt that you're actually getting a message that the cache is full. I think that you're actually seeing a message that is warning you that the current space allocated for your disk cache is too large for the free space on your computer such that _if_ the disk cache were to take up all of the space that you've allocated, then your disk would be full (or very close to it).
This started happening with the last update for 2014, and then became more frequent with the 2015 update. I tried backsaving it, and I could not get it to work.
Here is the error message that I get every morning.
And the cache folder is set to the iMac desktop that I am working off of. I have plenty of memory left on my computer. We just had them all serviced and defragged. None of that seemed to make a difference. But I would not think that that cache could be filled up with 60 GB in one day. I am wondering too if this is affecting the way my AE is preforming. I am having several issues with my RAM preview as far as it being incredibly slow and not displaying camera animation until I save and restart AE.
How much free space is on your iMac's hard drive?
That message is just saying that it doesn't have enough space to fit 93 GB safely. A hard drive should always have 25% free, so even if the drive has 95 GB free, using 93 GB for your cache isn't a good idea.
If you change your preference to allocate a smaller amount for AE, that message will likely go away.
And I could easily see the cache being 60 GB in a day. AE works in completely uncompressed frames. So, if you import a very compressed video file (say, an MP4), AE is caching an uncompressed version of that which could easily be ten or twenty times larger than the original file is.