Splitting up large file that gets bogged down does not work

I have made a voice recording that is 50 minutes long. Saved as one file seems to be too large for my laptop because when I edit it it is too bogged down and takes a long time for each command (cut, paste, etc.) to perform the action so I highlighted the second half of the recording and Cut and Pasted it into a new file.
What happened was the first half of the recording is easy and fast to edit, but the second half is just as slow as if it had never been reduced in size and is taking forever to edit.
When I run my cursor over the first file’s icon it says the file size is 416kb, and the second file says 1.79mb when it should be about the same as the first one.
What is going on here and how can I correct it?
Thanks for your help.

You’re still editing the Project. Projects are magic.

You can go back to the original show, highlight the first half and Export Selection As WAV…


Then go back to the original show, select the second half and Export Selection as WAV…


You can edit your brains out with those two individual wave files–each well under half the size of the original project–and then recombine them into a final show later. Also see: dividing up into thirds or quarters.