Sounds like the poster is having power management issues. Could be a dirty fan or a bad chip. I’ve dealt with the latter and it was fixed under warranty.
I've been using a MacBook Pro 2015 for a while now for my personal stuff - it's been nothing but reliable for everything from programming to surfing the web to DJ mixing. Just recently, the battery cycles exceeded normal usage and I got a notification from the system that the 'Battery should be replaced soon' - almost as soon as this happened, I experienced random slowdowns, freezing, etc just doing low-intensity tasks like browsing this site. Open up Activity Monitor and find that the 'kernel_task' is absolutely throttling my CPU. Long story short, this particular MacBook Pro had a battery recall and Apple replaced mine for free - worked just like new after that, which I'm grateful for since it's basically the best laptop I've ever used.