We go to Mexico 2-3 times each year. And every trip we dive the cenotes at least 2x. Usually Dos Ojos. The water EVERY time is 75 degrees F. I dive a 3/2 full and I am fine. My buddy uses a 3/2 shortie and is fine. There are snorkellers there in the same water with just swim trunks on. So your 3/2 shortie should work just fine. If you do dive Dos Ojos, they have wetsuits there for rental. So if you get there and want to rent some, they are cheap. They also have a box of well used and worn wetsuits for sale during our last visit. They were $10. So rather than buy or lug extra protection down with you, spend $5-10 on a rental of a heavier suit for the 1 dive. But unless you are doing multiple repetitive dives, a 3/2 shortie should be fine for the 1 or 2 tank dive you will do. On the other hand, I have some extra insulation too! I strongly recommend bringing a bug repellent and apply it about 10 minutes before you arrive the cenote. It takes a few minutes to take effect. Good luck.
