This is something I've also encountered. I'm running off of a MacBook Pro as well and have recently began picking up projects that require editing in Premiere. Although I'm ecstatic about being able to edit footage natively and not having to store duplicates that have grown exponentially in size due to coding, I'm slowly dying inside at having such a slow response for playback.
Rendering hasn't helped either, it'll make it smoother for the first few seconds (even up to a minute, if I'm lucky) but after that, it's the same old story.
Lisa Talley
Sacramento Video Production