If you find that Adobe Premiers has slowed down a lot it is probably because you are running out of Disk Space. Adobe Premier Pro caches all your Video Files and has a bad habit of not clearing them all out when you are finished.
Adding more RAM (memory) at this point of time will not help, in fact it could slow Premier Pro down even further as the more RAM you have on a system the larger the installation will be. In Windows 7,8 or 10, a normal install with 4Gig of RAM is about 28Gig, 8Gig of RAM 32Gigs, 16Gig of RAM 40Gig, 32Gig of RAM 54Gig, while if you go to 64gigs of RAM, Windows installation may exceed 100gigs. These numbers grow even more as you do windows updates.
For Premiere Pro to work at its best, it is important to have plenty of fast disk space, you will find that by clearing the Adobe Premiere Media Cache Files can help a lot....
In Premier Pro start by going to EDIT - PREFERENCES - MEDIA (as shown above)
The above Dialog Box should open and you just need to click on CLEAN and let Premier Pro do the rest...
To keep Adobe Premier Pro running at Maximum speed it is best to place the file you wish to edit on an SSD Drive (if you have one) and also to keep your Scratch Drive also on an SSD. If you have a large enough SSD you can use it for both, altenatively you can have a second SSD for these purposes.
To check and set your scratch drive options......
In Premiere Pro click on FILE - PROJECT SETTINGS - SCRATCH DISKS
The above dialog box will open where you can select your Scratch Disk options.