Hi, Running openhab 1.8.3 today on a ubuntu server with dashing and mosquitto MQTT server on today and that works good. I have a lot of items (about 160 KNX devices and some items for the MQTT rules.)
If I upgrade to 2.x will it run on a RPI3 or is that too slow for my configuration?
Actually, after doing some testing with 1.8 and 2.x on rpi3, I found no sensible difference!
So, don’t worry about openHAB 2 on a rpi, it will work as well!
First: You should definitely upgrade to openHAB 2. A huuuuge deal of improvements were added since your version last saw an update 
Secondly: openHABian and the RPi3 are a pretty popular combo-solution for openHAB. It’s used by thousands and seldomly creating any real issues. The RPi is quite capable and I wouldn’t worry about performance, even if you got a few more items. I made good experience with openHAB 2 on a RPi1B+ or lately with the cheaper RPi0W (and small OH setups) and those are considerably weaker.
Thanks I’ll try it.
Is it easy to upgrade the openhabian to the latest snapshot?
Just read what has been suggested:
and
http://docs.openhab.org/installation/openhabian.html#switch-openhab-branch