What can I do if my wife wants to file for divorce and I found out she's a felon and she used me for 15 months until her ex-boyfriend got out of jail

The fact that she's a felon will not affect anything, since California is a no-fault divorce state. However, you should consult with an experienced divorce attorney to help protect your rights and assets.

You have a choice: a) you can file for annulment, asking the court to erase the marriage as if it never happened; the process will take about 18 to 24 intensely unpleasant, nerve-raking months and cost you upwards of $5000 (depending on how determined your wife will be in fighting against the judgment, $10-15K is a likely range - but not the limit), plus couple of dozen days you would have to take off work; or b) you can give her an uncontested divorce (hopefully, she would walk away without alimony and pieces of your property and retirement funds), be free of this marriage in 6-8 months for about $1500-$2000, and chalk all this up to experience.