1.4 Gateway and 1.5 Sensors?
I'm reasonably sure I built my MQTT Gateway early last year so it must be running 1.4....
Will it be possible to use sensors with sketches that are part of the 1.5 version?
Yes - that should not be any problems - I did for a while before upgrading my ethernet gatewat,
Luckily it works great since my controller (fhem) not yet support EthGw v1.5.