I had 50/35 plan for years and I recently found that the actual speed was 15/0.2. Verizon sent me the technician two times to solve the issue. After two visits and 6 hours spent on the issue by a technician, the speed came up to 50/2.5. The upload is still not solved yet. The technician said the building I live uses DSL, not fiber, and the maximum I can get would be 10 Mbps. He suggested me to downgrade the plan then I will get the upload speed up to 10mbps.
I downgraded my plan to 15/5 by paying extra $5/months than my old 50/35 plan, and I tested the upload speed again. It's 15/2.4 now, which is very depressing result that I essentially paid more to downgrade the plan by following the technician's advice for the same speed. Verizon should higher my upload speed to 5mbps as supposed to be, or I will soon drop my membership after being a customer for 5 years with Verizon.
I believe you are using DSL and not fiber optics (Fios) the speed you are saying you had used for years and the downgraded speed of 15/1 brings me to believe your not using high speed Fios internet.
that speed test site you gave a link to is not for DSL customers but Fios subscribers.
so that Test is absolutely worthless.
Find out what service you actually pay for and call verizon to have them test it from your home.