Hi Learning Development,
I'm happy to help! If your video buffers when played from Vimeo, it may be a good idea to download it and insert it into your Storyline slide. Storyline videos have a maximum file size of 2 GB. You can compress the video first before inserting it into your project, making sure not to sacrifice the resolution, depending on your need.
If you are concerned about the learner's wifi connection, use the adaptive video quality to deliver video content to all learners, regardless of internet speed. Please don't hesitate to reach out if you have additional questions.