My 15 month old has started pulling her diapers off after she goes to the bathroom.
Could this be a sign that its time to start potty training??
It could be, however 15 months is quite early.
Potty training is all around the child's awareness that they are about to have a bowel or bladder movement, which takes a fair amount of learning whereas what you are describing is a dislike of the sensation after these have happened.
You could encourage your child to come to you rather than remove the nappy themselves. This would still work, and would certainly help to minimise mess.
It could be. It could also be a sign your 15 month old is interested in this new thing she knows how to do, or simply that she's aware the diaper is uncomfortable. It's a good sign that she's aware she has gone, but the bigger part is the ability to hold her pee for a period of time. If she usually has a wet diaper after naps, she's likely not ready yet. 15 months seems early to me for potty training, but every child is different, and I've heard earlier.
(For that matter, in less developed countries it's common to potty train extremely early - as early as 6 months - so who knows.)