Exporting 50k entires to wordpress db

hey guys ,
So i have a databse with 50k entries , i have been running a blog like 4 years but it was a custum cms build by my friend , now i am migrating to wordpress.

I am using wp_post_insert to insert queries into the database.
*I am tryign to insert all the data using a loop.

Now after 12k entries my script has goe\ne very slow , size of databse has gone upto 600mb , and still i have a log way to go.

My data is in a separate databse , and wp installation is a separate databse.

these are the 3 queries which i am using to insert insert into the databse.

$post_ID=wp_insert_post($my_post, $error_msg);
add_post_meta($post_ID, ‘description’, $desc, true);
add_post_meta($post_ID, ‘keywords’, $tags, true);

Installed , WP Super Cache but my script gives me a error.

What are the ways , by which i could increase the performance of sql queries.

Any suggestions advice would help me a lot.