$200k equity in home 2.75% int. rate - HELOC for stock investing?

[Ryan Jones]

We put $200k down on our home two years ago, 15 year 2.75% fixed rate. (really for peace of mind because I know I could earn more elsewhere)  However, unless Trump is impeached this year, the stock market will probably be earning another 15-20% (I earned 20% in 2017).

Is a HELOC the most common way to go here? $150k HELOC should be about 3.25%? Then I still keep my fixed rate 15 year mortgage payments + owe interest on the HELOC right? But I'll probably be earning ~15% - 3.25% owed? Am I on the right track? Yes I know there is risk, but probably not too much this year as it's a great market. Thoughts?