https://wildfiregames.com/forum/topic/36934-civ-differentiation-athens/?tab=comments#comment-419889
Taken from this thread.
Athenians were known to be a civilization that values education, so this bonus attempts to reflect that.
A problem is that while all the values work ingame, the Structure Tree displays every technology with a 15% discount, so P1 and P2 technologies show a 15% discount. I suppose it's better than every tech showing a 5% discount as it can be argued that they can be skipped until P3. Although, phase up upgrades can't be skipped and the structure tree will show them as cheaper than they actually are.
I'm sure that wording can also be improved.