We bought ours new and watched it being built at the factory. It will be 22 years old in June. and is just now showing sign of old age. Needs roof work due to a leak and the siding has several stress cracks. I will fix the roof leak and seal the stress cracks. Otherwise it still looks like new inside and out. It gets used for 3 to 4 days every month along with a 3 month stay at our favorite RV resort during the summer. Longest trip was a 7000 mile round trip to middle America.
Our previous TT was 16 years old when we sold it and it was still in great shape.
So if you maintain them you can expect more than 15 years.