While $1.5b is definitely a huge amount, take note that $1.5b is just a very small percentage of Alphabet's total assets/investments. Though I'm not ruling out the fact that they might be into crypto, them investing $1.5b doesn't automatically mean that Alphabet is "ready to take crypto seriously" or something like that.

There's a good possibility that Alphabet is just playing it smart and allocating a small percentage(basically hedging) into crypto-related companies, just as a sort of insurance for if crypto actually becomes far bigger from here and not just a temporary fad.