I'm creating a video of my kid for the year 2015.  It's currently about 2 hours and 40 minutes long.  When I load a small 2 minute .mp4 video to append to the movie, it takes about 20 to 30 minutes to actually load the file, so I can edit it.  I'm using an Asus 17" laptop with i7 processors and 16GB of RAM.  The laptop is several years old, but it was top of the line when I purchased it.   I tried deleting all of the files in the %temp% directory, and that helps, a little.  Very little. 

Is this slowness inherent to the large size of the movie I'm editing?  Anything else I can do to speed things up?  At this point it's almost unusuable.

Please add your exact computer specs (see mine below as an example) to your User Profile or Signature. Saying "i7" doesn't help. What specific model.

What is the source of your video files? What created them?

How much space do you have on your editing hard drive? 

PS needs a very powerful PC. 

I have an old ASUS 17" ROG gaming laptop with an i7 (2nd gen) and 16Gb ram and Geforce 970 graphics. Fact is that my backup desktop which has an i5 (4th gen) is faster. 

I'll assume you have SSD's.

I recommend you check if your original source video is higher quality than 1080p and 30fps.

2-min 4K 60 fps files would take an extremely long time for my i5 to swallow, and would choke it more often than not.

For me, 1080p 30fps is just fine, so I would convert anything with higher quality to 1080/30 before even thinking about introducing it to PSU.

Shotcut is nice and lightweight and you can use it to export your original videos into a more bitesize formats before serving them to PS, that was my solution anyway.