Reindexing documents

We're planning to upgrade from Elasticsearch 1.7.1 to 2.2, however our indices did not pass the Migration checker test. We have indices with Fields with dots ( Dots in field names lead to ambiguous field resolution ). We think the only way to fix this issue is to reindex all the documents. We have 10 Billion documents, 12.15TB Data, 16 nodes.
We're planning to build a new cluster and reindex all the documents to it.
What is the best way to accomplish the reindexing?
How long will it take?
Greatly appreciate the feedback

I use

As long as it takes, hard to say really . Depends on your node specs, your version, your document size etc etc etc