I expect that BA15/16 are far down the list of lucrative routes. They have a lot of VFF traffic and redemptions. Bear in mind too that the length of the flights 20+ hours, mean that they represent excellent value for J travellers, but a poor return for BA (plus the planes sit idle in SYD for around 10 hours). I wouldn't be surprised if there are some east coast US J fares (7 hours) that will be greater than some of the J fares sold to SYD. Plus it's a market with heavy discounting, especially in economy. So it probably makes sense to keep the better aircraft for the premium routes (JFK etc).

However, I think all BA planes should have well maintained cabin interiors and think this is something BA could improve on. I suspect over recent years slowing the rate of deep cleans has helped it survive more difficult spells, but think it shows on some aircraft.