Alter table fast

Hello,
It's postgres version 16.1, we want to convert an existing column data type
from integer to numeric and it's taking a long time. The size of the table
is ~50GB and the table has ~150million rows in it and it's not partitioned.
We tried running the direct alter and it's going beyond hours, so wanted to
understand from experts what is the best way to achieve this?

1)Should we go with below
Alter table <table_name> alter column <column_name> type numeric(15,0)
USING <column_name>::NUMERIC(15,0);
OR
We should add a new not null column.
update the data in that column from the existing column.
drop the old column
rename the new column to the old column.

Regards
Veem