We recently moved into a house where there is cat5e wiring running from a telephone jack in each room, to the rear of the house near the phone junction box and electrical box. The wires are literally just hanging out of a sealed exit point in the siding of the house, not running into a box of any kind.

I wanted to set up a new wired network connection from an upstairs bedroom to the living room. New wiring installation is virtually out of the question, thanks to insulation, fire blocks all over the place, and the fact that the wife and I both don't want to mess up the drywall in our new home. So I have chosen to repurpose two of the cat5e wiring runs into one connection, by splicing the two appropriate wires together out back. I wired up a cat5e jack using punchdown connectors both in the living room and in the upstairs office, and just hand-spliced the wires together out back and tried to weatherproof them by passing the splice into a weatherproof cable box and securing them with strong electrical tape. They are untwisted for about 3-4 inches and are sharply angled at the splice point. I know it's not optimal but I wanted to at least see if what I was after was even possible given the unknowns of the wiring, etc. 

Upon testing, I can get a solid connection over the line, so I know I've done the wiring correctly (used T568A due to the fact that these are originally phone lines and might be again one day). However, tests show that my download speed from my computer, connected to the router upstairs, to a laptop in the living room is only around 23 mbps, so I'm barely even getting fast ethernet speeds. I'm hardly expecting gigabit, with run lengths and connections like this, but what can I do at this point to increase throughput? There are factors I know I can control (how the splicing is done out back) but I don't know how much of a difference that will make. Then there are some variables like proximity to 110V lines in the walls, and quality of cable (it's all UTP) that are either unknowns or out of my control. I do know that the wires out back are fairly brittle, due to weathering, which is part of the reason I didn't want to poke around with those much. Does anything stand out as a glaring issue to anyone experienced with cat5/6 networking?