Hey mate,
So first a question: you mention an ssd: is that internal or external? If external, what connection are you using?
If you are working from an external ssd, unless you have it connected via thunderbolt, you should transfer the file to the internal disk. This is because the usb connection is too slow.
That said, the major issue is the file format, mp4 (i’d assume H264). That is a terrible format to edit, as it is heavily compressed. Thus, DVR has to work a lot to unpack the information to work with for every frame.
The best way to solve the issue is to use either proxies or optimized media. If you are not working with other editors I’d recommend the Optimized. Anyway, the resolution can stay to choose automatically, the important setting is the format. I’d recommend DNxHR HQ if the source is 8bit or HQX if the source is 10bit.
With the optimized/proxies you’d be good to go.