Is $15,000 to replace roof a fair price?

I just had my roof replaced last week. My insurance company has already paid me the full amount (minus my deductible), and I'm waiting for the invoice from the roofer. I told him I would mail the payment after I receive the invoice and have the work inspected. He didn't seem happy about this. I know nothing about roofing and want to spend a couple hundred dollars for an independent professional to inspect the finished work and confirm I received what I paid for, as $15k is a lot of money. My house is about an hour away from me. My insurance company called me late last year saying my roof needed replacement based on satellite pictures. An adjuster did the estimate, and my insurance approved the amount. I asked the adjuster for recommendations and picked the highest-rated company. I gave the roofer the insurance estimate, and he agreed with it. He replaced the roof the following week without asking for a deposit or contract, just a phone chat. I found this strange. My insurance company is dropping coverage in my state. My agent told me after a storm that I needed to replace the roof because they saw damage, giving me a heads-up so I could get it replaced and secure coverage with a new company. I'm now covered by a new company, and the underwriter has photos of the new roof and is waiting for the invoice for final approval. My new insurance bill lists an inspection cost, so I think they will send someone to check too. I also emailed town hall about getting someone to inspect for code compliance. The insurance adjuster cut a check for the entire amount upfront, which I found unusual but was happy about. I guess they sometimes split payments, but they didn't with me. The roof has been replaced without a contract, just a verbal agreement that I'd pay after getting the second insurance payment (which I explained I got in full upfront). I just want someone to tell me it's okay to pay after ensuring the work was done properly. I feel the roofer is more at risk having done the work without a written agreement, but I obviously intend to pay him. I am illiterate when it comes to trades work, but my word is my bond, and I want to get him his payment ASAP after confirming the work is correct.