Well, there is a bit more to the price of silver (and gold) than there is to bitcoin and lesser cryptocurrencies. Silver especially is an actual resource in industrial production, used in all kinds of electronics, including electric cars and solar panels.
The historical 15/1 ratio applied in a time when silver was pretty much only decorative, used for cutlery, mirrors, and jewelry and I believe it was more of a function of society and of specie-backed currencies.
Now that large industries can't go without it, different factors need to be considered, I think.