[Question] OTA Update

Hello, so I have an ASUS Zenfone 2 (4GB Model). And everytime an update comes out, I download the firmware wich is basicly at least 1 GB and I have to flash my device and lose all my data everytime an update comes out. But now I heard of a new way I could use wich is OTA Update. And it is basicly a lot less than the firmware size, and it also won't make me lose my data. The question is, when I want to apply the OTA Update, let's say for example I'm runing 2.15, and the latest one is 2.18. Do I have to update each OTA version seperatly until I reach the latest one? Or directly skip to the latest one?