Hi Dave, Congratulations on the purchase. That's low miles! Good call to swap out fluids. If the previous owner neglected to drive it they may have also neglected to change out other fluids too like the coolant and brake fluid.

As far as conventional vs. synthetic, I think you're fine as is with conventional for now. You might consider a synthetic in the future as the Volvo modular engine (you have the 4 cylinder version, not the more common 5-cyl or 6-cyl) is said to stay cleaner on synthetic lubes, especially when turbocharged.

The best advice you may get is to consult the owners manual for Mother Volvo's guidance on the matter.

In the meantime, enjoy your new ride.

-Will