@ojipog from my understanding no school can require you to give a decision before April 15th, due to a grad school resolution that all schools signed. If you accept one school,then get off the waitlist for another school and want to accept that second school instead, you are required to get written permission from the first school before you can accept the second school. Here is a link to the resolution with the official rules: https://cgsnet.org/april-15-resolution
Some schools, (i think Salus is the only one), did not sign this resolution which means if you negate on the acceptance you are not required to get written permission in order to accept another school.
I suggest you call the school you are currently waitlisted with and ask about your place on the waitlist. Explain your situation to them. If there is a good chance you could get off the waitlist hold off on giving the first school a decision until just before April 15th.
Hope this helps!