RE: Dell Inspiron 15 Gaming (7567) + external monitor = (performance) problems
Thanks for posting.
Apologies that your computer is not working the way you expected. Other users with a similar issue as yours have reported success by updating the BIOS and/or disabling Turbo Boost. You might try those to see if it resolves your issue.
Here is some information you may find helpful: http://dell.to/2y6sGN3
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