AGM or Lead-Acid?
IMHO 15.1 seems a bit high.
Have you come to any reason why you have been killing batteries?
Is it bolted down correctly?
Is it exposed to excessive heat?
Is it in a daily driver?
The 15.1v could be part of the reason
My current O'Riley average battery is coming up on 6 years, and around 12,000 miles. (Longest lived battery I have ever had)
Most of my newer cars batteries last around 5 years, 7,000 to 8,000 miles per year.