do I have to report 1099-k income from renting my timeshares? They were rented for less than 15 days. Where can I find the answer in from the IRS documents?

No, you do not need to report this rental income.

The IRS says in this document:

There's a special rule if you use a dwelling unit as a residence and rent it for fewer than 15 days. In this case, don't report any of the rental income and don't deduct any expenses as rental expenses.