people may have realized who Clinton really was before March 15

Wait, are we seriously pretending people weren't keenly aware of Hillary Clinton as a politician before this election cycle? She's easily one of the most well known politicians in the last decade, staggeringly so. She's had mud thrown at her from every direction for a really long time (not even trying to imply she doesn't deserve it).

The problem wasn't that people didn't know Clinton earlier, it's that they didn't know Sanders earlier. If he would have been this aggressive the entire time he'd have less supporters, not more. A huge part of his campaign strategy was curating a public image that he was above all the political nonsense and just wanted to get in there and do a good job. Now that it's clear he has no path to victory, the message is changing from "I'd make a great president" to "The DNC is broken, we need to shake things up." It's a good message to be sending.

If Sanders would have started building name recognition before the election season was already in swing, if he had built the network of enthusiastic young voters before the first primary, he could have had a different outcome. By the time people were really pushing with him, he had been treated like a distraction for way too long to catch up. He started an important conversation, but his campaign was pretty mismanaged - especially early on. You can't really blame them though, I don't think they expected to do nearly as well as they ended up doing - or bringing in nearly that much in donations. Much of his campaign ended up being last minute maneuvering (but again, how could it not be given that financially they were flying by the seat of their pants).