The only applications that require libKF5Baloo5 here are Dolphin5 and Gwenview5 (and Plasma5 itself, for the config module, KRunner and the Application Launcher I suppose).
And you can keep the library.
But I’m not sure if Plasma 5’s Baloo seaech will work with the KDE4 indexer…
I’ll have to be patient.
KDE:Applications 15.08.0 has been submitted to Factory 3 weeks ago, but it’s still stuck in staging for some reasons.
You might want to remove KDE:Applications again when 15.08.0 hits Tumbleweed though.
KDE:Applications is the development project for Factory/Tumbleweed, you get everything in it via the standard repo anyway (just some time later, after staging/testing).
The situation is similar with KDE:Extra, but this one also contains some additional software that’s not part of the standard distribution.