Oliver was 15mos when we brought his baby sister (same mom, different dad) home at 8weeks. At first he wanted nothing to do with her either, but it only took him a couple of days until he was romping and playing with her. Just be patient, it will happen. I did the same thing as the others are telling you, give the first one lots of attention and let them know they are first. I sat on the floor with the two of them and just let them be near each other. Now they are best buds...always together!
Good luck!!