I'm using the same gateway (T3200) and I am on copper (25/5), not fiber optic, and my latency on a speedtest is far lower (wireless, cell - 6ms, wired PC, 4ms). Your latency should be lower than what you're seeing unless you're testing to a far away server or there is something on your network interfering.
Something still seems off with one or both of your connections. I'm on a bonded connection (2 lines) also and my latency is much less. If you log in to your modem, click on Status at the top, what does it say in the table on the right for your Downstream and Upstream rates? First page is the combined total. Same question if you click on "Line 1 Status" and "Line 2 Status" on the left column.
Are you located in a city or a smaller town?