100,000 * 160 = 16,000,000. Some messages will be longer, other shorter than 160 characters, but overall, 18 MB doesn't sound unreasonable. If you are really paranoid, make a backup of the entire folder ~/.rtcom-eventlogger. Especially the file el-v1.db. Open X-Term and run
Since, as you say, you have made a full backup of everything else, you may as well proceed with the update without too much worry about losing anything.

As to how to get the communication history to the S4, I have no £$%&ing idea try qwazix's suggestion.