What, exact, version of CC 2015 are you using? Some of them (particularly 13.5.0) were rather buggy.
It could also be due to your unfamiliarity with the previewing process in AE.
You can't expect it to perform like a video editing application because it isn't one.
It says version 184.108.40.206.
At uni I used an older version on AE and no experienced this.
The preview options in the newer version of AE aren't all that different from the RAM preview of older versions. You just have more control now over how the preview behaves. Look at the preview panel and how you can set it up to behave differently based on pressing spacebar vs. 0 vs....
I suspect the difference may not be in the version of AE, but the hardware with which you were using it then compared to now.
Can you share a screen capture of how it's behaving so we can see if it's being unusual?
I meant a video rather than a still. If you don't already have software for it, I think ShareX is freely available.
From your screenshot, I see that you are hobbling yourself a bit. Set your resolution to be auto.
Since you're working at 25% zoom, you can work at quarter resolution without losing quality. Setting your resolution to Auto will do that automatically. Then, when you need to zoom in for something up close, the resolution will adjust to match.
To easily work at the most efficient resolution set the Comp Panel resolution to AUTO.