What confuses people more, changing from 21 million to 21 billion or asking people to buy a coffee for 0.0015BTC? Imagine when BTC reaches 10,000USD, a coffee for 0.00015? really?

It's just redenomination, it won't lose value. People are not used to deal with infinitesimal values. And for most people, they couldn't care less how many BTC total are there.

If Bitcoin wants to be used by the masses, it needs to become more similar to their realities.