Lightroom CC: Smart Previews required? Option to not keep them?

I was wondering how much the new cloud-based Lightroom CC would take available disk space when using it as a native macOS app interface to my Synced Collections in LR CC 2015 but couldn't find any details about it.

So last night I installed new LR CC to my Late 2013 MBP 13" Retina with a 256 GB SSD, in LR CC app preferences changed Local Storage > Storage Strategy for Target Available Disk Space Usage to 5 % and let it sync. This morning I'm now seeing this warning message:

Low disk space: please clear some space or change your local storage settings.

Looking at Finder the Lightroom Library.lrlibrary file is 28,27 GB in size. Looking inside this package:

• "Managed Catalog.mcat" file takes 1,14 GB
• "originals" folder 0 kt
• "previews" folder 59,6 MB
• "proxies" folder 27 GB
• "settings" folder 247 kB

So "proxies" folder is taking the most of the storage space with 27 GB. Inside "proxies" folder there's another folder called "2560" so I'm assuming new LR CC keeps 2560 px size Smart Previews locally.

My photos on new LR CC (synced photos in LR CC 2015):

• 28.914 photos
• 27 GB Smart Previews

Am I assuming right, new LR CC needs to keep Smart Previews of all synced photos? If this is true, could there be an option to not keep Smart Previews for all synced photos?

What I'd like new LR CC to be (for now) is a macOS native app interface to my Synced Collections and photos so that I don't need to attach my external SSD drive just to be able to browse my synced photos (and I don't have to have an internet connection as browsing via LR Web would need).