Is >58 hours to create an index normal? Should I cancel and try again?
What is the value of sort_buffer_size?  200M might be reasonable on your machine.  (A sort might be involved in the index creation.)

Keep in mind that it will rebuild all the indexes.  Still 58 hours is unreasonable.

What is the value of innodb_buffer_pool_size?  It may be using that.  It should be about 11G for that size machine, assuming you are using only InnoDB.