Timeline with Effect = Problems! Timeline with NO Effects = No Problems!

[Edit Head]

Hello folks this one is for real!
I have a long haul (10 years) doc film in the edit that has taken everything I've had over the last decade to bring forward.... beaten by gangs, imprisoned, divorced and almost went bankrupt last year but I believe in what I do and somehow a ray of light always shines through and the finish line is slowly making itself visible.

The project is now sitting at 6 hours on one timeline. With the effects applied, I hit play anywhere on the timeline and the associated external drives all begin to light up one by one, PPro thinks for a moment, and then begins to play. But it's laggy. Over time, the Mac's memory is eventually eaten up and the system has to be restarted.

Conversely, with all the effects removed, the project file reduces from 20mb to 5mb and I can skip to anywhere on the timeline and PPro will play instantaneously.

I want to see the film I'm building with the effects applied - as I'm sure others do. Why is it that with the effects applied PPro is constantantly talking to the source drives (click click click) and when I hit the space bar, PPro mostly needs to light up all the drives before waiting 5 seconds to play wherever I park the cursor? But with the effects removed PPro is lightening fast.

The Project was started in PPro 2014. I'm now on the latest version of PPro, 2013 Macbook 10.14.2, ProRes

I've reset permissions, deleted cache, imported the project into a new project but the problem persists.
Question? Is there a 'known' legacy effect (or plugin app) that can cause PPro to become laggy upon playing?

OR... is this normal PPro behavior???

I would really appreciate some professional suggestions/ advice?
Thank you.

[Justin T - Hyper Brew · Accepted solution]

Premiere has changed a lot in the past 10 years. So while effects may still exist and appear to work, a lot of stuff is legacy, outdated, no longer supported.

You have 2 options moving forward. If you edited majorly on a specific older version of Premiere, download that specific version and finish the project in that version.

Option 2, more painful but probably the best way forward would be to re-create all the effects with the up-to-date versions.