From what I've seen on this forum, I'm doubtful an Apple Store will actually perform any repairs in the store although this could vary by location as it seems they mail it to their mail-in repair depot. Even if repairs are performed at the store, it is doubtful they will have any parts in stock at the store and would need to request a part from their regional warehouse.
Plus if this actually a 2015 model, those were discontinued back in April 2016 and is considered "Obsolete" according to MacTracker app. Apple does not perform repairs on products classified as "Obsolete" although Apple's documentation at one time mentioned battery replacements could go for as long as 10 years after a product being discontinued, but I have never seen this happen for anyone as they do have in the fine print "as long as parts are available".
Obtaining service for your Apple product after an expired warranty - Apple Support
I think at this point if you need a battery for this laptop, then you will need to source one from OWC or iFixIt. However, the quality of third party Lithium Batteries is extremely poor even when purchased from even these two respected vendors. With many of these Apple laptops professional installation of the battery is recommended to prevent accidental damage and to ensure battery "calibration" is carried out properly.
