I am also 6'5" and 225lbs, and ride on 23's with no problem, plus when I started I was close to 250lbs. My bike came with Schwalbe Durano's which are a mid tier tire, nothing special, and I rode them until they wore out inflating the front to 100psi and the rear to 110psi. I made the switch to tubeless which allows you to run lower pressures and now I'm running Fusion 3's inflated to 90psi front and 100psi rear. I have always seen a slight bulge in the rear tire and always thought it could be low but after checking it was spot on so I never worried again. I would think running a larger tire would actually make the tire look softer? More sidewall to deform? You may also want to make sure you are balanced on the bike properly too, being a new rider I would bet you are set up a bit more relaxed, upright, and back which is okay but the higher up and back you sit the more weight is distributed to the rear of the bike. For me I started that way and within a few months I had flipped my stem, removed all but one spacer on the head tube and moved the seat forward a touch. All of these adjustments made me and my bike more balanced resulting in a better ride and a lot more comfort. I'd say don't worry yourself so much about the tires, air them up to at least 100psi front & 110psi rear and enjoy the ride. Maybe start thinking about your position on the bike? If you paid someone to fit you then maybe ask for their advice first before making any changes and take note of where everything was before you start moving things so you can go back to square one if it doesn't work out. I'm by no means a bike fitter or tire expert but these are things I did to improve my ride and myself. Good Luck!