ON EDIT: Thanks to all who posted below who corrected my "BAD MATH". Concept correct, math not so much. Rather than leave questions, I will edit to supply, as others have done the correct answer: 430 AH @ 12 VDC.
The 20 hour rate is the most common rating.
So, each of your batteries is 215 AH @ 6 VDC. So each pair wired in SERIES is 215 AH @ 12 VDC.
Both pairs together (your battery bank) is 430 AH @ 12 VDC.