This is absolutely bizarre. It is not a nice surprise it is deeply unpleasant that he didn't discuss the idea with you beforehand. He is not acting like a father!
Some of these responses are crazy. 'Deeply unpleasant' to book a holiday with your wife, but without your child?!
Listen, the fact of the matter is, your baby is barely out of the 4th trimester at the moment. It's 100% natural to not really be able to see a time in the future where you'll be comfortable leaving him with anyone for any sort of period of time.
And it genuinely is different for men (maybe not all, but certainly a lot of them) as they haven't had the same physical connection you have with their child. Also, maybe he's just more forward thinking? It doesn't really matter, he's just thinking he's booked this lovely romantic trip away for his wife that he loves, has made arrangements for your shared child and you're not quite happy about it.
I think what is plain is that it's different strokes for different folks - and just because there are some showing sad faces at leaving their kids behind doesn't mean it's wrong or bad. PS I didn't leave any of my kids so much as overnight until the youngest was 5 so it's not like I've been gallivanting a lot!
My advice would be to tell him you're not sure, find out the latest cancellation date and take it from there. Maybe see if it's possible to postpone for another year. But the likelihood is that by 15 months you'll be quite all right with it.