S.D.
I knew as soon as I read the last post that it was Cheryl without even reading the name, lol.
Of course it's your fault, but don't let it get you down. There's nothing wrong with teaching a baby that you are there for her! A few weeks ago someone else asked about CIO and was told it was harder on you than on the baby. I like to compare it to an adult situation. Let's say your husband said one night "I'm leaving" and tried to explain why using mostly French. You caught a few words, mostly they were "...love you...sleep...night..." Then he walks out leaving you to cry yourself to sleep. You don't have any concept of time because you can't read a clock and all you know is that you are alone when you usually aren't, you're cold when you usually have someone to snuggle with...You call his cell phone over and over but he just won't answer. Who do you really think it's harder on? You or him? This is how your baby sees it except being 15 months old, she hasn't had time to build up years of trust like in your marriage.
The point is, cold turkey is never a good way to do anything and that's what the CIO method is, sudden deprivation for a little being who just doesn't get why.
So, take a few nights, maybe over a weekend when you don't have as much to do during the day. You and hubby take Friday off and start Thursday night. Put her down and when she wakes up, once of you go in, pick her up to settle her, as soon as she's not drying, put her down, pat her back for a bit to make sure she's not screaming again and leave. If she cries, give her 5 or 10 minutes and go back in to repeat. It can be exhausting, but it works for the moms I know who have tried it.
Just as many people will say CIO works as will say it doesn't work, so if you want to go that way, go ahead and try, but it's not the mirracle cure that believers tout it to be. It also works much better from the beginning than all of a sudden at 15 months. So, if you had been able to let her scream when she was 2 months, it might work now, but you have taught her (rightfully, in my opinion) that you will be there when she needs you and that's hard to unteach.
A few good books on the subject:
"The Baby Whisperer"
"The No-Cry Sleep Solution" (for babies)
"The No-Cry Sleep Solution for Toddlers and Preschoolers"
"The Sleep Book" (Dr. Sears)
Good Luck!