Cat5 wiring parallel or series

I have two workstations. From telephone line master socket I run two 15 meter cat5 cables in the opposite directions. I assume broadband signals levels are divided between two locations. I have been told I could connect them in series to improve signal levels available. Is this true for both locations? Can I convert the existing installation by using a spare pair from one location to return to the master socket and then fed to the second socket?