Just to share my experience, I flashed v11.5 without doing full wipe coming from v11.1. The new LP9 firmware appears to be very much smoother in overall performance.
I guess I am lucky, no issues for me without doing the full wipe. Had tried install apps from file manager, install apps from play store, restored user apps from titanium backup, tested wifi and most other function, everything just works so far..
The only exception is what some users encountered with fc on the dial pad. As posted by someone earlier, clear data on contacts and contacts storage solved the problem (all my contacts were gone after cleared data but were immediately auto restored from my Gmail contacts).
I had originally done full wipe on my first flash with v11.5. But I had problem with apps fc after data restored for my user apps from titanium backup. As I can't restore data back to whatsapp, k9 mail and a few other user apps, I had thought of giving up and to go back to v11.1.
Eventually, I nandroid back to v11.1 and flashed v11.5 over without full data wipe and got lucky.