Can I change from 15D to 153A before I ship for basic in 9 weeks?

There is a lot more involved than simply changing your MOS to become a pilot. Besides taking the SIFT test (no longer called AFAST) and a flight physical, there is a lot of paperwork involved and you still need to get Letters of Recommendation. It's actually called 'street to seat' and it's not something you just sign up for like an Enlisted MOS.

At this point your only real option is going through with Basic and AIT, then putting your packet together to apply for 153A. You can knock out certain parts of it while you are in AIT (since you'll be at Eustis) like the SIFT test and get most of the paperwork done as well (USAREC 3.2, DA Form 61, etc). Then once you graduate AIT and make it to your first duty station get the flight physical, DA photo & LORs done and more or less be ready to submit your packet.

Not really. Technically, it could be possible to back out of your enlistment and apply to WOCS, but then you'd be ineligible because you'd require a waiver for your discharge. 153A isn't an enlisted MOS, you have to apply to a board that meets a few times a year and they select the most qualified applicants. You're looking at something like a one year time line from starting your packet, submitting it in time for the board, and the selection results being announced.

What you can do is attend AIT, meet some pilots, get the required letters of recommendation from them, and apply to be a pilot once you pass the SIFT.

NO- 1. To become a Warrant Officer, you must attend a Warrant Officer School, (Apply and be accepted) to apply (Warrant Officer CAndidate) you must be enlisted in the service, because if you fail the course they will return you to your unit/old MOS. Until you enlist and graduate AIT you will not have an MOS to return to.