From Premiere Pro User Guide > Hardware and operating system requirements > Hardware recommendations for Premiere Pro and After Effects

Upgrade Premiere Pro system in this order of priority:

1. Add more RAM – up to 128GB if the motherboard supports it (especially for long-form content) 
2. A faster GPU – or additional GPUs for faster export and rendering with Premiere Pro
3. For storage: Faster (or additional) SSD or NVMe drives
4. CPU with a faster clock speed
   
   

So, increase your RAM.  Also, use a format that is good for video editing (like ProRes 422 LT) with storage media with sufficient capacity and speed.

Delete the Media Cache and Media Cache files:
https://community.adobe.com/t5/premiere-pro/faq-how-to-clear-your-media-cache-in-30-seconds-in-premiere-pro-2020/m-p/11017257/thread-id/260446?page=1

If that doesn't work, try creating a new project and import the old one into it.

Have you tried proxies?

https://creativecloud.adobe.com/en/learn/premiere-pro/web/proxy-media