Boston, MA here and I've also been getting similar speeds to what you posted. Download speed plummets to 12Mbps late afternoon and then 2-3Mbps at night with a 25/2 plan.
I've had this problem before, but it went away. It started back up yesterday or the day before. Was it the same for you?
Let me guess u have a docsis2 modem. Get a docsis3 modem and u will have more consistent speeds.I spent $45 on my own on eBay and get advertised speed even during peak time.