Bitcoin Core client upgrade from V0.7 2-beta to latest 0.15.X (Oct2017) - ‘wallet.dat’? I need to apply an upgrade to my Bitcoin Core client From V0.7 2-beta to latest.

I've got some advice that I need to make that upgrade a 2 step process 
(i) V0.7 2-beta' TO Bitcoin Core 0.14.2 
(ii) Bitcoin Core 0.14.2 to Bitcoin Core 0.15.X 

My questions is regarding my ‘wallet.dat’ file in this 2 step process.

Does the wallet.Dat file need to be put back in AFTER phase (i) and resynched ? 
OR 
Can I put the wallet.Dat file back in for the first time only after phase (ii) and synch ? 

Cheers
You don’t need to touch the wallet file (but back it up), the format hasn’t changed and is safe to upgrade on top of.