I read an article somewhere that Benz recommends uping
the 15 to a 20. This car has two fans , so draws even at low [ a/c high pressure ] speed.
The high is in the temp circuit and requires the 30 as fast speed is a bigger draw.
As far as the egr code , pull a vac on it with a hand vac while at idle. If it run rough when you do, the port[ infamous port] is not plugged.
There is a change on this model egr. If you find it is the valve, email me for the literature on the new change.