I'm in Tulum right now (November 2016). I would assume the worst if you're staying on the beach. However, in town you can find a good connection on the main road. I'm at Campanella Cremerie and getting 30/down 10/up with a 6ms ping on their wifi.
There's also 4G now with a Telcel sim. However, you have to be on the main road or very close to it. On the main road with my Telcel sim I'm getting 20/down, 20/up, 50ms ping, but I've been a few blocks away where I can't get 4G or even decent 3G. So it's really hard to say where you'll get a good signal.
I wouldn't count on getting a good connection on the beach, especially as you move further south. However, I'm sure you can find a good connection if you search for it. I had 4/down with the wifi at Diamante K the other day which was pretty good. Other spots I've tried on the beach were unusable.
Just so you know, a lot of the best beach spots/restaurants are deceivingly far from town, so I would make sure you consider that since the appeal of Tulum is the beach. IMO not the best place to learn Spanish either since the default is English in so many places.
FYI: I've only been here a few days so take it for what it's worth.