Macbook Pro Slow

Hi guys, I have a 2019 15 inch Macbook Pro - i9 with 16gb RAM & 512gb SSD. I'm finding it extremely slow. There's hardly anything on it, I keep all files on an external SSD & only keep files on the Macbook that I'm currently working with. I haven't even used over 100gb of the on board SSD yet. I cannot use Premiere Pro without it literally lagging just to scrub through a file with images. If premiere pro is open I can't even use chrome without the macbook momentarily freezing.

I'm finding this absurd because I had a 2012 MBP - 13inch | i5 | 16gb RAM (DDR3) & 120GB SSD of which I did the internal upgrades myself (RAM & SSD) and I got way more performance out of that than I'm currently getting on this machine. Any suggestions ?