Re: Importing dump of huge table takes forever since 5.6.15

[Rick James]

You really should be switching to InnoDB from MyISAM.

The xx.MYI file contains the index(es) for the MyISAM table xx. ENABLE KEYS rebuilds the keys from scratch, which is likely to be more efficient that building them while inserting the rows.

The more INDEXes you have, the longer the rebuild will take. Let's see SHOW CREATE TABLE; we may be able to advise you on removing some redundant or unuseful indexes.

If you do a SHOW PROCESSLIST during the rebuild, it will say either (something like)
Reindexing by keycache, or
Reindexing by sort
The latter is likely to be the case, and likely to be faster (for big tables). If it is using the keycache, let's look at your settings (SHOW VARIABLES) to see what might need changing.