On UE 4.14.1 this method dont work, now to increase your streaming pool size by default you need to go to C:\Program Files (x86)\Epic Games\4.14\Engine\Config\BaseScalability.ini scroll down and you’ll find the secction with TextureQuality@0, TextureQuality@1, TextureQuality@2, TextureQuality@3 and TextureQuality@cine ,(every secction has its own Poolsize value) in my case, my pool size was set by default to 1000, so i identify that seccion TextureQuality@3 got pool size value to 1000, so i change it to 2000 and save. thats all.
To change the Pool size inside the engine(Running EU4) open console and type r.Streaming.PoolSize _2000 (IMPORTANT!!! between the e letter of Size and the Low line must be a space)