You say you're halfway, but you still have about 150 characters left to introduce?? Idk how deep you're into the story in terms of chapters or whatever, but to me it kinda sounds like it'd be a nightmare to introduce that large of a cast in the later half.. At that point, I'd personally reconsider whether all of the characters are important enough to be in the story at all... but again, I don't know how long the story is, so there's a chance it could work if it's a super long series.
If you have to keep all of them in, I'd introduce them in groups and focus on a select few, similar to how the anime Hunter x Hunter would do it for each arc. You introduce them quickly and establish who they are, using cliches and tropes if you have to, but the main ones that have an influence over the biggest points of the plot are gonna be the ones you'll wanna focus on the most. I'd highly recommend giving these characters some type of character arc, if not a strong sense of personality. There's no guarantee you'll be able to make the biggest, diverse, and most memorable cast where all of them are equally developed, in my opinion. A huge amount of them might have to be "filler" characters if you go this route, but this is your safest bet in introducing them quickly and effectively.
If you find yourself thinking that like.. not all of them are that important, consider cutting down the amount of characters you're gonna wanna add in the future, but don't abandon your leftover characters completely! You can always reuse them for a spin-off or even a separate story in a different world altogether! .The smaller the cast is, the more chances you'll have for mostly everyone to interact with everyone in some way.