I'm getting ready to buy a 48" walk behind, but I don't know which size engine to get a 15 HP or 17 HP. Both are Kawasaki engines. The 17 HP is about $500.00 more than the 15 HP. Is the 15 HP going to be enough or I am better off going with the 17 HP? It is a Snapper Pro, hydro drive if that helps.