How many words is typical for a 15 month old?

My daughter has approached all of her milestones early except for talking. I am the only one home with her during the day and I try to talk to her alot. We have started doing flash cards and I ask questions like "gs or puffs" but she would rather point or grunt. She will shake her head yes and no most times. But she does not like to speak. She say's bye bye alot and I have heard her say ball, fish, mama, tank-u (thank you) but it has not been in the last month and it was only a couple of times. She is great with directions. I can tell her to take her pants off, open the hamper, put them in, and then close the lid. And she will do it all without me having to repeat myself. Same with her diaper (except in the trash). But I am starting to get worried with her speech. Any suggestions on how to get her talking more? And how many words do children this age typically know?