Combined MPG sign of issues?

[Bmwtvboy]

Recently, these past 3 months I have noticed a decline in my mpg. I used to get a combined H/C of about 19 and always 21 on HWY.
Now I see 18 combined and the last couple of tanks 15-17 mpg range.
Using 91 octane. Regular oil changes 5K/w filter. Syn:5/30 No burning oil
issues. Still accelerates smoothly but lately some rough idle at start up.
Ideas of where to start looking? O2 sensors all four changed out at 160 , now214,800K Original top end engine components. Disa valve and CCV unit replaced around 160K.

[Ricky Bobby]

Is it the AC working extra hard in summer perhaps?

[Bmwtvboy]

I'm in Maine so I haven't used the A/C since leaving FL back in May. It worked fine all the way. I had put a new pusher fan in which works great. It even kicks on now and then after shutting off the X. Blows for a minute or so and then shuts off. NO overheat problems. No coolant leak.

[O3X5]

how many miles currently on the spark plugs & air filter?

[Bmwtvboy]

Got the codes today: P0014 = Over advanced exhaust
P0015 = Retard exhaust side
Sensor
SO, is this definitely just replace the vanos seals?
There is a solenoid and another sensor; do they have to be replaced?
When I am in there is there anything else I should look for to replace?
I would like to get more miles out of the X
I am changing over to coil rear next week.