Wordpress merge multiple sites into one multi user site

I have about 15 standalone instances of Wordpress. Each using a different woo theme that has been customiz开发者_运维技巧ed and some plugins.

Is there an easy way to retain all plugin and theme settings when migrating to wordpress multisite?

Try to follow Migrating multiple blogs Codex page recommendations. But if you have different customized versions of plugins on your sites - it seems you are in trouble then...