Compare tiny capacitance using comparator
The smallest general purpose electronic capacitor in the world is 0.1pF. \$=10^{-13}~F\$

Your requirement so far does not have any merit as \$
10^{-15}~F\$ is only 1% of this.

Unless you can define your dielectric, conductor geometry and purpose, nothing close to what you suggest is suitable.

You are asking how to measure capacitance less than two 1mm square pads separated by 1 meter.

try something else.