That's strange. I have similar specs on my MacBook Pro and have not experienced issues like this.
What kind of vector files? Are they very large or complicated?
What size is your composition?
Is your composition set to use the Classic Renderer or something else?
The composition size is 1920 X 1080.
I don't consider the vector files to be large or complicated. They're pretty simple, with no gradients or other big surprises. Stuff like the image below.
(In the past, I have used larger vector files, with gradients & fine details, and everything played smoothly in the Preview up until we got to AE 2017.)
The renderer is Classic.
Are you still facing this problem? If not, let us know how you solved it. If so, please let us know so we can assist you further.
No, it is still happening. I used RAM Preview since around 1999 until it went away, and I can't tell you how much I miss it.
As far as RAM preview goes, you can have AE set up so that it behaves the exact same way as the old RAM preview system did. The new preview panel has a LOT of options in it!
As for your issue, it sounds really odd. Again, my similar MacBook isn't experiencing those problems. Would it be possible for you to share your project file so I could test it a bit more closely to what you're doing?
Also, try installing and working with an older version to see if it behaves properly. (Remember, your CC subscription includes every version of AE as far back as (and including) CS6 and you can install them all alongside each other without issue. So, you could have CS6, CC, CC 2014, CC 2015, CC 2015.3, and CC 2017 all installed alongside each other if you wanted to! )
How do I set up RAM Preview so it behaves like it used to?
I believe it defaults to replicating the old behavior as is. So, if you press the numpad 0 key, it should do what it did before. That is, it should cache before playing back similarly to the old behavior.
Basically, you can go into the preview panel (make sure you pull it down to see ALL of the options). You can change how the preview behaves with each different keyboard shortcut and customize it to the way you like to work.