The main effects are:
-British troops tied up in the Orient are freed up and will be transferred to the Balkans.
-The opened Straits link Russia to its Allies. This might considerably help
-Bulgaria remains neutral; increasing Entente pressure on them, Romania and Greece to join the war and open a link to support Serbia. If Serbia cannot be subdued, Austria-Hungary will have a three-front-war for longer than they can take it
-Russian Army gets rid of the burden of the Kaukasus front, more focus on the main front; some farmers can be released back into civilian life
-the US will mobilize and start fielding an army during the course of 1916; that means: for the planned offensives of 1916, Britain and France can use heir manpower recklessly to grind the Germans down, assuming that if they don't manage, the US will finish the job in 1917
-blockade will tighten after US declaration of war, another malus for the CP
After these "good news", the CP don't stand a chance. Starting negotiations still in 1915 would be the wisest thing to do. The longer the war takes, the worse it gets. If the CP wait until they are beaten militarily, I assume that over the course of 1916 they will get to the breaking point. If revolution doesn't break out, their military will be crushed in the spring offensives of 1917 - at the VERY latest.