Yeah, 15'2 is not huge (and personally I like shorter horses although to each own). I do consider slant for exactly same reason - so I could just tie the divider and let my horse to use whole stall (still to have 2 stalls if I must haul both of my mares, because things happen).
Just curious... Do you trail ride him or you show as well?
"Life isn't about waiting for the storm to pass: it's about learning to dance in the rain..."
"When we are no longer able to change a situation - we are challenged to change ourselves."
"How people treat you is their karma; how you react is yours."