Long-time lurker here. This sucks and I'm sorry they're doing this to you. Temple similarly pressured me (asking me for my "likely decision" 1-2 weeks after sending the offer, which would mean I'd be deciding without even getting to go to their open house--and they wouldn't allow me to freely talk to a student). I did some googling around this at the time because I was trying to figure out how to respond--though I ultimately just declined the offer because I have a better one at Ohio and had such a bad feeling about Temple from these communications.
Some advice I saw was to reply to that pressure by gently reminding the school about the April 15 date and that you have the right to wait until then to make your decision. If they're on this list (https://cgsnet.org/ckfinder/userfiles/files/CGSResolution_Nov2019Revision.pdf) they should be abiding by that date, and not pressuring you. I also think based on this page (https://cgsnet.org/april-15-resolution) that if you accepted their offer before 4/15, you could then change your mind and decline (also before 4/15) and be technically fine and following the rules, though it's obviously not an ideal situation.
I guess one thing I'd be thinking about as well is whether you want to go to a school that puts this type of pressure on you to decide early. I got such a bad feeling about Temple when they did this, and it seems that you have some other good offers also on the table. This might be telling you something important about the program's culture, unfortunately.