You can do service yourself and still maintain warranty. I do. Save any receipts for parts (like oil and filters).
Checking the fluids, rotating tires, and checking the floor mats (!) and whatever else is required at 15K shouldn't be a problem if done at 18K.
Checking the fluids, rotating tires, and checking the floor mats (!) and whatever else is required at 15K shouldn't be a problem if done at 18K.