It should, yes.
That being said, some RAM simply doesn't 'play nice' with other RAM modules or kits. Sometimes it'll work straight away, sometimes it requires a little added voltage, sometimes it simply won't work at all.
I've never really had much issue 'mixing and matching' myself, but plenty others have - a quick search of posts on this very forum will throw up lots of results for mixing & matching causing issues.
An easier solution (assuming your board supports it) would be a new 'kit' of 2x8GB for your 16GB, but you'd likely be fine with the 2x4 + 2x4, but just know there's no guarantee.