Is 85 minutes reasonable for a Schengen to non-Schengen transfer?

I have a United Saver business reward that includes legs from ZRH to FRA 09:35 -- 10:35 then a flight to LHR at 12:00. Also I think the arrival gate is ASW which means a bus from tarmac to the concourse rather than a jetway. That plus the UK passport control line I'd need to get thru has me worried. Will my "business class" ticket help at all with the passport control line? Because of the tarmac bus sitting in the front won't help at all timewise.

I'm not that concerned about luggage because this is at the end of a trip so if my bag shows up two days late it's no biggie.