If you can average 15% a year, your account will double approximately every 5 years (excluding new contributions). That is a reasonable goal but you may have to dodge a few corrections to do it.
That means in 15 years you'd have about about $600K, and $1.2M in 20 - without new contributions. So with contribution included, you might be OK, although inflation will get you.
If you can squeeze out 20% a year (very tough) you would double every 3.6 years. So watch out for those bear markets.