15 tons of gold... well, for comparison, Spain sent about 500 tons of gold to USSR during the Civil War, supposedly to get weapons, and it wasn't nearly enough.

I would submit that, if your answer is essentially "bring 15 tons of money" then a proper answer to your original question requires at least an outline of how you're going to spend that money in 1918: how you're going to arrange purchases, who you're going to buy from, what you're going to buy, how you're going to move the purchased goods and the money, how you're going to protect them both at rest and in transit, and how the purchased supplies are going to change the outcome of the war.

So if you're going to buy guns, for example, which manufacturer are you going to buy them from, which model, can they actually supply the model you want in the volume that you need in 1918, how are you going to get the gold to them and get the weapons back, and then which parts of the army are going to get those weapons and how does that lead to defeating the Russian army.

Otherwise you're just bringing 15 tons of liability.