Sky is a MVNO, in other words they don’t have their own masts but use those of one of the operators who do. Their website is strangely coy on the subject, but as far as I can see (Which?, Wikipedia, …) they use the O2 network.
This is important, because in most cases, the roll-out of OS updates depends largely on the technical network, not really the commercial one. You might want to contact Sky and / or O2 to find out more about the delay.
You might also get in touch with Fairphone Angels in the UK who may be able to help with information Hanworth, London, Edinburgh. Click the blue spots on the map for their respective Heaven e-mail addresses.
Please also read about FP5 updates to A15 in particular here and here. Especially, if your Fingerprint sensor is not working I would strongly advise you to wait until a corrected update is made available.
[Edit - removed a sentence that might be interpreted as “hearsay” and that adds little except my own opinion.]