Save the date problem.

Hi Hannah. If your save the date didn’t specify I wouldn’t worry about it. Although you can also get save the evening. You may find that not everyone will come. Maybe send your invites out in batches. The first lot need to be in by a certain date (maybe a quick turn around) and then another lot by the next date. Then you may not need to worry. Do you know why your venue reduced the numbers?

It would be worth asking your venue why they have reduced the number you can invite. If it is to do with something you have added to the reception (e.g. table layout, photo booth etc) then it might be worth seeing if you can rework things so that they can take all 90.

Otherwise, I would contact the 15 you can't fit in and apologise, explaining to them that you will send them a whole day invite if enough people drop out.

The issue with saying nothing and hoping that 15 of your first batch of invitees can't come is that if they all accept, it's going to be very close to the wedding date by the time you tell the last 15 that they are only invited to the evening. And by that point, they may have turned down other invitations under the impression that they are spending the whole day at your wedding. So I think it would be better to be up front about the issue early on.