I got a quote abour replace slate roof. contractor said need $15

my house is 44 year old, single level, 1278 sf SFH in San Jose CA. I didn't plan to replace but home inspection said my roof has some wear out. then I asked my general constractor how much if I replace the roof. he said matariel is expensive, so it will cost me labor+material $15,000. the new roof can last 30 years, so each year cost me $500, as he said. tommorrow he will chekc my roof.