i did ib through high school
math is easy as you should honestly go for lower level unless you really feel you excel in math
science i took IB physics, which was.. pretty god damn hard, but I toughed through it
languages i took spanish, pretty easy considering you didnt have to really know it just how to recognize key words and get the gist out of a paragraph
history is what concerns most people, but as long as you stay ontop of your shit and study, you'll do fine.
english was where I faltered, my senior year english teacher was a massive poetry buff, and bob dylan buff. every fucking day i would walk into class and he'd have us compare this poem to a bob dylan song, worst experience of my life, also would fail you on persuasive essays unless you wrote exactly what he wanted even though the goal was to state your side
IB is honestly great because you get free credits depending on where you choose to go to school, and you learn to effectively study and manage your time wisely
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as for my tf2 career, I honestly am not good at tf2 and probably won't ever will be, but I live on the west coast, and with Theory of Knowledge (TOK) happening for me after school from 3-5 I couldn't scrim with my team until around 8:30 EST, which is usually on time for like half a scrim before your matches start (i played shitty steel highlander and rang for 6s teams)
tl;dr - IB is fairly easy as long as you manage your time, and it shouldn't affect your TF2 career too much, but if you want to get ample time in for scrims you might want to consider getting used to 3-5 hours of sleep a night
oh and don't cheat they'll kick you right out of the program and you will not recieve a diploma or anything (had it happen to a friend of mine who "CHEATED" on a research paper). like don't even try to cheat, they check all papers for plagiarism using shit like turnitin.com (which cross checks your paper across the entire internet, and against papers already turned in)