2 G3 Class Battlecruisers (16 inch)
2 Admiral Class Battlecruisers (15 inch)
2 Renown Class Battlecruisers (15 inch)
5 Queen Elizabeth Class Battleships (15 inch)
5 Revenge Class Battleships (15 inch)
6 King George V Class Battleships (16 inch)
Now the above list does not include losses of which there must be some, nor does it take into account that some ships may be disposed of earlier, the Renown and Repulse for example, or that some other sort of capital ship may be added between 1930 and 1940, possibly a group of "Treaty" ships with 14 inch guns.
Also the RN in TTL will have had control of the FAA since 1923 at the latest and so will be more "carrier friendly" with at least eight large aircraft carriers in commission by 1943, again baring losses.
Now that I've written it down I can't see that Vanguard would be built even if the turrets are there. The RN here has three extra BC and one extra BS for use.
I think the KGV's were meant to replace the R class due to the fact that they had limited upgrade-ability, which gives you a timing problem due to the London treaty and fitting 16" gun's. but I don't see how with extra existing battleships and carriers that the RN could fund a 14".