Your engine runs on fuel and air. That's why it is important to keep your engine breathing freely with a new air filter for your 2015 Subaru Legacy. Aftermarket air filters allow for greater air flow and improved performance compared to OEM filters, meaning you can make this regular maintenance item into an upgrade. Increased air flow can prolong the engine's life and increase power output, and these performance filters last longer than factory filters too. Check your owner's manual for exact intervals, but generally you can ensure maximum efficiency air flow by replacing your 2015 Legacy's air filter every other oil change.