Possible causes of oil in the coolant are leaking headgasket, leaking intake manifold gasket or oil cooler.
If a headgasket, you are looking at around $3500 parts and labor
If the intake manifold, around $1200 parts and labor
If the oil cooler, around $400 parts and labor.
Of the 3, the headgasket is most common.
For this, I would suggest paying $100 for a block test to be performed. This tests for combustion gases in the coolant. IF positive for combustion gases, it is the headgasket and I would walk away from the purchase
P2015 is for the intake manifold runner, which means replacing the intake manifold at around $1600 parts and labor.
Personally, with these issues I would walk away from the deal.
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