To be fair I haven't yet seen a broken promise from O2 regarding lollipop updates,
@Chris_K has been very forward with any info available. You've got to remember it's the manufacturers that set the updates and In regards to lollipop, both Samsung and Sony flagship updates were first available to O2 customers.
In regards to z ultra, it hasn't even been certified yet, nothing to do with O2 but Sony. I suspect the length of time between Z1 and Z series will be longer than Z3 to Z1 based solely on the fact the SOC'S on z1,2&3 being so similar thus easier to adapt.
With the Z series, it's gonna take some more work to get lollipop running nice and as intended, the Z series is where Sony are being very generous in the fact that most other manufacturers wouldn't bother supporting the older system.
It's gonna take a bit of time longer than you'd hope but I would say a fortnight to a month or possibly longer.
Either way, it is coming just be patient.