levelling combined floors for new wood floor

[jimbob147]

Old house. Two front rooms previously knocked in to one. Both concrete floors "level" but one ~15mm lower than the other, so is a region of ~10cm sloping lip at the threshold (to be honest, it's a bit of a hump). Now, I want to put down a machined wood floor down across the whole space - glued down not screwed.
Do I:
(i) pay £200 for 20 bags of self levelling compound to bring the lower floor up to the higher one
(ii) rent a floor grinder to try and make a much more gradual slope between the two thresholds and hope the wood floor sticks down to this bit
(iii) put down 15mm ply across the whole of the lower floor, with a bit of self leveller to fill in the gaps
(iv) your option here!

Any advice, very gratefully accepted….

 

[gregers]

why cant you use some self leveler on the low side and run it out then use the ply over the lot?

 

[jimbob147]

cost, that's all. By my reckoning, the option of mostly using ply to bring the lower level up will cost ~£120, but the self leveller will be twice the price. Self leveller then ply on top of all would be £300 all in…..
I guess my question is, is bringing up a floor with ply and gluing a floor down direct on it as "good" as gluing a floor down on cornet/latex. Or could it cause problems in the long run?