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?

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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...