I use Canon Raw, Lightroom Mobile on the iPad and all the necessary gimmicks to get it working (cloud sync and smart previews, I'm tired just of thinking all the fiasco that is needed).
When I modify any image in Lightroom Mobile and export it to camera roll it is stripped of all metadata. Not even the date it was taken is kept in the file.
Is this a bug or a "feature"? Considering how embarrassing and complicated it is to use Lightroom Mobile and the hours of upload needed to get my photos in the iPad I wouldn't be surprised if Adobe told me it is meant to be like this.
Let me make it clear: stripping metadata won't save a lot of bandwidth, but it takes me back to the year of 2000 (literally, my photos without a taken date become marked as taken in 1st of Jan of 2000 by a lot of softwares).
I hope a "fix" for Lightroom Mobile is delivered in Lightroom 6. I can't work like this.
In LrM, go into the options - you tap the Lr icon in the top left. Then look down to where you see Share Metadata and choose the option you want.
You don't need to think about smart previews, so that should take a weight off your mind.