Hi. The short answer to your question is going to be it depends. California Code of Civil Procedure 703.140(b)(10)(D) does not set a dollar limit on what you can exempt (save), but rather allows you to exempt amounts generally considered "reasonably necessary for support." (see the statute for full description). Generally speaking what is “reasonably necessary” is dependent upon your jurisdiction, the Trustee assigned to your case and your particular circumstances. The safest course of action may be to exempt out what you can with the wildcard exemption and then exempt out the remainder under 703.140(b)(10)(D). Feel free to contact my office if you have any further questions.
I agree that the safest way is to use the wildcard exemption because it can be used on any type of property and is totally safe. The term "reasonably necessary" can always open you up to a dispute with the trustee.
If you have enough wild card then use that first. You should speak to an attorney on this.
I agree w/ the other attorneys that it is probably best to use the wildcard, unless you need to use it to protect other assets. That said, as a practical matter, if you did use (b)(10)(d) to protect the support your are owed unlikely that the trustee would challenge $15k. It also depends upon what trustee you have, of course.