It all depends on what assumptions you can make about update frequency and the continuity of link.
If you can't assume 100% availability of the link, but you need to maintain operability in between link uptime windows, it's worth paying the price for a sizable data file download, and perform runtime deserialization of that in the abscence of uplink.
Remember:
The network being available should never, ever be taken for granted.
DOn't forget that JSON isn't only a web interchange format.