Very tough
In this era, there are many more competing powers than in the post Great War era, and too many powers that can destabilize things easily. If Britain and Germany come up with a treaty, all well and good--until it looks like Italy and France might go to war, or Austria-Hungary's fleet grows, Suddenly, Britain's interests in the Med are threatened--new ships needed. So Germany builds some new ones.
Then there's the USA. I can't see the USA getting tied up in a treaty at that time...so Britain needs more, so Germany needs more. In short, almiost any, even relatively minor, nation can throw the balance off. Tricky to pull it off, and would need some serious statesmanship--in the 1920's, there were only5 battleship-building powers, with little prospect of war in the near future...