Research: 

If you would like to research your DNA results further, you can join the R-L21 Yahoo Groups forum.  There are excellent researchers and well-informed laypersons that can help you understand more about your known or speculative haplogroup. 

R-L21 Yahoo Groups forum

R-L21 Plus Project

FTDNA Walk the Y Project 

Also see the R-L21 Haplogroups webpage to understand where your known or speculative project fits into the list of R-L21 projects. 

Other excellent documents: 

file: R-L21 Tree 20100927 - Alex’s R-L21 Cluster Tree (see files on the R-L21 Yahoo Groups)

South Irish is listed under 1511-A-T2 on page 24.