How long is the project?
What is the resolution of the bulk of the source files?
What are the export settings?
Have you tried exporting at a lower resolution?
Someone here will be glad to suggest or make a fix if you take a few minutes to share your project. It's easy to do and can be private. Just follow these steps...
1. With your project on the timeline, click on MENU at the top-left. Click FILE|BACK UP PROJECT FILES TO FOLDER. Choose a folder and SELECT FOLDER.
2. Locate the saved, numbered folder. No need to upload the export or VPJ files. Upload it to a free server - Google Drive, MS OneDrive, etc.*
3. Get a shared, public link. If using Google Drive click GET SHAREABLE LINK. Change "restricted" to "anyone with the link can view" Then click COPY LINK | DONE.
4. Paste that link here, or click the folder at the top-right of this forum, and privately message it to me. It won't be shared.
* Before uploading, right-click the folder, click PROPERTIES. Look at the File Size to confirm that it's not too big for the free space on the server.