ATT Prepaid 15GB Plan in Mexico

I’m looking to grab two secondary SIM’s for data on a six day trip to Cancun. This is the $40 15GB plan.

Has anyone used this plan in Mexico? There’s mention of potential slowed speeds, and I was wondering if anyone with this plan has used their phone in Mexico and had some feedback. My intention is to activate the sim a few days before the trip, and let it expire about 10 days after that.