The 315's will be fine on the front, but the spacing required so they don't touch in the back may not be there.
You can play with air pressure to get a better ride. No reason to blow them up to the max. But you don't want them underinflated either.
Mike in Colorado
2004 Fleetwood Pace Arrow 37c, 8.1 gasser, (Jezebel) Ultra RV ECM / TCM, plugs wires, and rear track bar, PPE deep Tx pan, Bilstein's, Sailun's & Sumo's all round, pushed by a 2002 Grand Caravan, on a Master Tow Dolly.