S.L.
i used a little potty on my daughter when she was 22 months old! influence is great, it works! it took me 2 months of non stop training but she was completely off at 2 years and ocassionaly on every now and then. she is now 5.5 and since then i never used pull ups..she may have only went on her bed maybe a few times..i followed the rules about no drinks b4 bed time and things like that..
15 months is young but the sooner the better!
Good luck
S.