The rigid polycarbonate about 15 years, the 4year greenhouse poly you can stretch to 5 or 6 without problem usually. Amount of shade cloth and how many months out of the year will affect the durability of the plastic. The more full sun directly on the greenhouse covering the shorter the lifespan. The times I listed though are with full sun all day every day. They are quite durable to the UV.
Inflated poly also has it's own set of challenges though with keeping it inflated hehe