doc: release notes for 8.15
doc: release notes for 8.15

rnveach/checkstyle,romani/checkstyle,checkstyle/checkstyle,checkstyle/checkstyle,romani/checkstyle,checkstyle/checkstyle,rnveach/checkstyle,rnveach/checkstyle,romani/checkstyle,rnveach/checkstyle,romani/checkstyle,checkstyle/checkstyle,checkstyle/checkstyle,romani/checkstyle,checkstyle/checkstyle,romani/checkstyle,rnveach/checkstyle,rnveach/checkstyle