Replace battery in 2015 MacBook Pro at Genius Bar? (Retina, 15-inch, Mid 2015)

First, you should check to see if the battery is covered under Apple's 15-inch MacBook Pro Battery Recall Program. If it is, then proceed with the replacement process on that page.

If your MBP is not covered by the recall program, then contact Apple Support to make arrangements. They have both mail-in and in-store replacement programs. (But even in-store, expect it to take 3-5 days).

I do not recommend after-market DIY battery replacement. It is a difficult & dangerous procedure. Leave it to the pros.

Per this Apple service estimator, only the 13-inch 2015 Macbook Pro shows as one Apple will work on:

Mac Repair & Service - Apple Support

I doubt that any Retina Macbook Pro battery can be replaced in-store any more. The batteries in Retina models are glued to the underside of the top deck and cannot be removed without toxic, flammable solvents that cannot used or stored in a retail setting without violating a laundry list of OSHA, HAZMAT, and fire code regulations.

Based on what we see here and service senior contributors have experienced, the store will most likely send the computer to a centralized Apple refurbishment for battery service. At their discretion they can replace the battery in a work-safe setting, or install a refurbished deck assembly that has a fresh battery.

In the US, the battery cost is $250 US IIRC assuming Apple still has the part available. I don't believe mail-in repairs are an option for laptops considered "Vintage" by Apple, so any Apple Stores or AASPs which perform mail-in repairs may not be an option. If those locations actually perform the repairs themselves, then they can do so if the necessary part is still available from Apple.

If a battery repair is not possible through Apple or an AASP, then make sure to get a battery from OWC or iFixIt. The quality of third party Lithium Batteries is extremely poor. Even when purchased from OWC or iFixIt, you may still find their batteries may not be as reliable as the Apple OEM batteries, but these are your best options. However, professional installation is recommended (OWC even has such a note on their product page) especially for the 15" 2015 model since it is impossible to remove the speakers without removing everything else in the laptop which increases the risk of accidentally damaging the Logic Board or something else since some cables & connectors are very fragile and the speaker connectors are really tight & difficult to disconnect. I have literally lifted up the connector from the Logic Board even when I've been extremely careful & aware of the possibility.

FYI, the third party Lithium Batteries do need to be "calibrated", but what is most important is making sure to allow the battery to charge to 100% & letting it sit on the charger for several hours after reaching 100%. Then use the laptop normally on battery power to let the laptop slowly drain the battery until the laptop powers off at 0%. Reconnect the power adapter and let the battery charge to 100% again and keeping the power adapter connected for several more hours after reaching 100%. Once you do this, then use the laptop as you wish. For some reason the third party Lithium Batteries tend to need that "calibration" in order to work correctly. I don't believe it is actually like the traditional calibration of older style batteries, but more of a way to properly "exercise" the battery initially. I've had issues with third party Lithium batteries where this "calibration/exercise" was not performed.

You can schedule a repair with the Genius Bar. Just go through the Apple Support link I provided earlier. ("Start a repair") The cost will be around $250-$350.