Yes, the waiver you mentioned is extremely hard to get even if you have some family members. It seems to apply for the immigration visa (I-485) again after 15 years is fine. But you should confirm it with immigration lawyer. Ask 863211 and Pijiang about it.
Another option is to talk to a good immigration lawyer. If you can get pardon for previous conviction, you will be fine. However, what is considered as a pardon? The official "pardon" defined in each state seems very hard to get and also takes time. Does expungement count? Maybe not. But anyway, you should consult with professional lawyers.
By the way, the immigration lawyer, esp. when it comes to criminal issues, may not be professional. You may need to do some research carefully before selecting one. At the same time, you should do a lot of homework, starting with google to see if there are similar cases before and what the procedures you are facing soon.
Another thing is immigration law is different from state law. As long as you have conviction, it will be always there no matter it is expunged or dismissed later or not. However, to make you convicted for a similar crime under immigration law, the elements of both laws will be compared precisely. You should do it by yourself first: find the definitions of both laws, and use the logic from what you have read to determine if it fits. Such questions can be risen up by lawyer, but eventually authorized by court. When you search online, you can see how the previous cases handled. But usually it's done this way on the appealing process, which means it will cost more.
