procedure in NY state to reopen modify divorce decree entered 15 years ago, appeal or motion to reconsider divorce decree

It would not be possible to have the judgment vacated after 15 years. You may be able to have those aspects of the judgment most harmful to you modified. For instance child support can be reduced upon a proper showing. So may spousal maintenance. Child custody and visitation may also be modified if a good reason exists to do so.

You fail to state in your question whatpart or parts of the divorce judgment you object to, nor do you offer any facts which would help someone whether a court would consider helping you. You need to give many more details to get a meaningful answer.

The Civil Practice Law and Rules provision that may be helpful is §5015 that governs vacating defective orders. §5015 does not impose a deadline for vacating defective orders but you have make the application before the same judge who issued the order. The three paragraphs that deal with typical matrimonial-based erroneous orders are these:

Rule 5015. Relief from judgment or order. (a) On motion. The court
which rendered a judgment or order may relieve a party from it upon such
terms as may be just, on motion of any interested person with such
notice as the court may direct, upon the ground of:

2. newly-discovered evidence which, if introduced at the trial, would
probably have produced a different result and which could not have been
discovered in time to move for a new trial under section 4404;
or
3. fraud, misrepresentation, or other misconduct of an adverse party;
or
4. lack of jurisdiction to render the judgment or order ... .

However, nothing in your fact pattern helps to identify what the defect was. So, you'll have to rely on modifications as were explained in the previous answer.

Lastly, do not start to make motions by yourself. This is not cooking scrambled eggs. Go to an attorney who can advise you based upon your particular situation and assist you properly. Do not take the law into your own hands.

First. I am not an attorney licensed in New York. Please consult with a family law attorney in your jurisdiction. However, Timesharing, visitation and child support orders can always be modified if you can meet standards for modification. This standard is usually substantial change in circumstances. I would need more information from you such as what provision are you looking to modify. Second, the right to an attorney exists only for criminal cases, not civil. You may want to go to the courthouse and look at your actual divorce file and copy the order that was entered in your case.