Use the latest version, if it's been less than six months since purchase.
Right-click in the preview window and change preview resolution to a lower preset.
Allow the green line above the timeline thumbnails to complete before previewing. The line represents the caching process.
Close all background applications while editing and exporting.
Share your project, if it's not a lengthy one, so someone can check it out. Here's how...
1. Save the project. Then, with it on the timeline, click the FILE menu. SAVE PORTABLE PROJECT AS to any convenient folder.
2. Open the folder that contains the saved files and ZIP them all.
3. Upload the zip file to DropBox, Google Drive, MS OneDrive or the like. It's free.
4. Make the uploaded file public (share it) and copy the shared link.
5. Paste the link into this forum.
Video editing is resource intensive. It's advisable to have at least 8GB of RAM, copious free disk space, and a fast processor such as an I5 or I7.