I hate to be Debbie Downer, but I've heard this April 15th deadlines is only for offers with financial support (https://www.cgsnet.org/april-15-resolution). Also, it depends on if the school signed the April 15th resolution.. here's a list of schools : https://www.cgsnet.org/ckfinder/userfiles/files/CGS_Resolution.pdf. I mean it covers basically every major school but if the school didn't sign this, I don't think they have to abide by the deadline...
Regardless, I think you should still talk to the school to see if the date is flexible and tell them about your situation. March 3rd is an insanely early time to decide where to go (like you said, interviews are still in full swing!).