You can turn autoplay off/on for playlists on YouTube. Refresh YouTube after toggling.
With this extension, when you reach the end of a video in a playlist, the next video is prevented from playing automatically.
Click the extension icon to toggle this behaviour on and off. Refresh YouTube after toggling.
Alternatively use the shortcut (ctrl+shift+y), which can be changed at chrome://extensions/shortcuts.
Source code available via my website.