Not GP, but there's no secret sauce here. VTSAX is up 25% each of the last three years, and it's hardly unique. The market has been doing well. Things that track the market will also do well.
The (US) market has done 11% annualized in the last 15 years. 20% is not just "traking the market". It's the difference between going from $1m to less than $5m or more than $15m.
Now, if "15ish years" means "12 years and 9 months, from the exact bottom" then yes, the annualized return has been over 18%.
