I thought After Effects had recently been given a re-engineered core designed for speed.
It's actually in the middle of being worked on. CC 2015 is just a partly done version of it. Some people are having great success with it. While other people...not so much.
Do you have CC 2014 on your machine? If not, get it and see how it behaves. How to Find and Install Previous Version of Adobe Apps in CC 2015
What format are these frames? Where do they reside (local hard drive, NAS, RAID, etc.)?
What effects are in use?
Is this a project you've built yourself?
When you're scrubbing, you say the RAM isn't filled up, but how do your CPU's look? If anything, I would expect to see one core spiking if it's a CPU issue. But if none of them are, the issue resides somewhere else.
Wait, quick question: is your comp accidently set to use the ray-traced renderer?
Thank you for your response. You are asking astute questions.
Effects in use are a photo filter, a few Set Mattes and a timer (all stuff I normally use without issue). I don't think it's effects-related because even if I just load the raw frames in the viewer (by double-clicking the PNG footage entry in the Project panel) it's still slow.
The files are PNGs (what I always use) and stored on an NAS (as always). As I said, this job is not unlike hundreds of others I've done in the past in terms of it's specifics. The project was built myself. CPU utilization does not seem to respond much at all during scrubbing as seen in the Task manager. Incidentally, video card is nvidia Geforce 980 Ti.
Raytrace is not on.
I will try CC 2014. That's a good idea. Hopefully it will be more responsive because right now 2015 is basically unusable.
Out of curiosity, could you try bringing files onto your local drive instead of the NAS and see if CC 2015 behaves as expected that way?
Also, let us know if CC 2014 behaves itself with both the local files and the NAS files.