Thanks for your reply, I will use a buck converter to power the Uno with 5v 
I'm sure I will blow the Uno with 15v!
Indeed I was wondering about voltage spike safety etc because it's not inductive I might not have to add more safety measures. Thanks for confirming.
I wasn't sure if connecting the grounds together would put my Uno at risk, that was my main concern, maybe I didn't make that clear in my post, sorry.