I did Modern History at A Level which included the whole of AS Level focusing on Russia.
It was ROUGH... lots to remember, I started at beginning of Nicholas II reign 1894 and went right through to Stalin's death in 1953.
It's likely your course could cover same timeline as so so much occurred - Tsarist vs Communist Russia, 1917 Lenin uprising and Russian Revolution, Bolsheviks and their opposition, then onto Stalin vs opponents eg Trotsky, Bukharin, Kamenev, Zinoviev after Lenin dies, A **** TON OF ECONOMIC POLICY which was grim honestly (this bit is what made it a difficult subject - five year plans, collectivisation), purges and red terror.
Oh and chuck two World War's in there from a Russian perspective - economy, political, Russian fronts and operations...
My advice would be take Russian history if you have a good memory, enjoy learning about economic policy and enjoy reading (I presume you like reading if you're considering Law or History at uni). Otherwise it is tough going in my opinion. That being said...it was INCREDIBLY interesting stuff which made it less painful to study than it should've been overall.
That also being said, the latest I studied Tudors was my third year in high school... I can't speak on any economic or religious policy in that time, which again i'm sure there is a lot of. All I know is Henry VIII, six wives and Break With Rome haha.
Also, I did a Masters in Law at University..... my A Level history I found didn't really equip me with much for this moving forward as once I went to university, writing and argument style changed quite a lot for essays I found. My advice would be to take the subject you think you'll find the most interesting in order to get a good A Level mark, this is honestly what matters most moving forward if you know you want to go to Uni. Good luck!