How much heat conservation?
Our do you have a nominal thickness of rock wool.
If so the just pro rata that thickness looking at the heat transfer coefficients of the two.
HTC rock wool about 0.03 to 0.04 W/n/K
Aerogel about0.013.
So half the thickness of rock wool?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.