Watch an in depth tutorial on: How To Fix Lagging Playback By Rendering.
Step #1: Make sure your entire edit is selected. You can do this by dragging your curser to the first frame of your edit and pressing “I” and dragging your curser to the last frame of your edit and pressing “O”. Once you are sure the portion of your edit that is lagging is selected you can move on to step #2.
Step #2: Hover over the “Sequence” tab on the top menu bar in Adobe Premiere Pro and select the option “Render In To Out”.
Step #3: This will start the rendering process. Once the rendering process is complete, you will be able to watch your edit without any issues and continue editing your project.