Based on fjtorres' experience https://www.mobileread.com/forums/sho...6&postcount=13
I'll try 15.1 tonight or tomorrow.
Did you experiment with various firmware versions?
EDIT: I've switched back to 14.2.
Yesterday, in the middle of my newest book (Conspirata by Robert Harris) 15.1 got stuck. I couldn't turn off, I had to do a manual reset. In the week before upgrading to 15.1, 14.2 didn't crash even once.