Yes, IPVanish will slow your streaming speed. This is because when you connect to IPVanish (or any other VPN), your traffic travels to an alternative server, resulting in minor slowdowns. IPVanish is quite fast, with an average speed drop of 37%. While that can be good enough to stream in HD, IPVanish is still slower than ExpressVPN, which had an average speed drop of just 12% in my tests.