Help on framing this picture...

I did this picture for a friend 6yrs ago and he has come back and aked me to get it framed for him. So i took it to the framer and he suggested i want to take about an inch/inch & a half off the right hand side (the picture17 3/4" x 14"). Maybe I am a bit of a traditionalist, but I thought it looked better with the horse centre to the picture, rather than it being offset? he said it would be "looking into the picture". He has way more knowledge than me and I listen to his advice but Im a bit wary of altering this to the point its irreversable. Any thoughts on what might look best?