You might want to run some speed checks (like at
www.dslreports.com for examlple) first to see how close you're actually coming to that 15 Mb throughput. Verizon's FIOS is totally affordable in 5 Mb and 15 Mb flavors, $40 and $50 respectively. But if you want to jump up to the 30 Mb connection, the price jumps to something crazy like $160 per month.
Also, if you switch, I will hate you. Just so you know. My 3 Mb cable connection is $47/mo. Don't ask me why Miami, damned FL is so backwards with broadband options. I was paying $45/mo for my 6 Mb cable connection in dinky little Cedar City, Utah -- a town of 30,000 people. I can go up to 5 Mb with my cable provider here, but it'd be $60/mo and I'm too poor.