The PC looks more than capable enough. My 2009 Sony Core2duo laptop with Intel Graphics does YouTube to a 1080p HDTV over HDMI just so sweet that in a battle of machines mine is just dust.
It can't be the i5 here at issue. I'd suspect the internet connection or your "protection" suite.
How about a WEB SPECCY?
Read https://www.piriform.com/docs/speccy/using-speccy/publishing-a-speccy-profile-to-the-web
And no to the disk space.
I have a 1070, the best i5 (im pissed at myself for not getting i7), 16gb ram, 2 tb storage, 240 gb ssd. Was working fine for a month now it sucks. Could it be because my ssd is half full and my 2 tb is 75% full? Thanks for the help!

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