Well my 2015 battery croaked this week too. It lost voltage a month ago and had to recharge it. It won't keep a charge so I'm in the market for a replacement like so many others here.
I don't want an expensive battery and a wet cell or maybe a agm type will do fine for me.
In my searches I found the following chart showing battery sizes. I looks like a 21 or 26 series is a nearly perfect match for the stock 2015 battery. I'll check out local auto stores and Walmart's tomorrow.
UPDATE: The 121R is taller and just barely fits into the space AND then only if you put the posts to the outside due to the + post being reversed. So forget this battery.
I'm checking one of theses first --
Everstart MAXX MAXX-121R
- 5 Year Warranty Program (3 Years Free Replacement + 2 Years Prorated)
- 600 CCA (Cold Cranking Amps)
$102.62†View OnlineMore Info
Everstart Platinum AGM H6
- 5 Year Warranty Program (3 Years Free Replacement + 2 Years Prorated)
$137.87†View OnlineMore Info