I am not so good with hybrids. A Rtm gets around 13'' maybe larger and a dovii can get up to 26'' or so in a large enough tank. I guess it depends on which genes are more prominent, if the dovii was father or mother etc...
Guessing I would assume that it will be over 15'' so you will need a large size tank for it. Cool looking fish though. I am not a fan of hybrids, but parachromis hybrids still keep that predatory parachromis look, so I tend to like them best out of hybrids. Aside from the Manaconda (managuense x festae) . The most beautiful hybrid of them all.