I am importing 2 hr+ video in premiere pro and it causing a lag and i am not able to do anything after and also some other 4k files also takes time to load properly before i can edit them.

You left out a lot of crusical data for a question like this. What exactly is the media … framesize/rate, and codec/format? Is it a long-GOP perhaps?

And what is it ‘residing’ on … internal SSD, external, network server, what? And past that, “Ultra 7” doesn’t tell us anything really … OS/CPU/RAM are always requested bits.