Update: I've sorted a script that returns the time of a half rotation. Apparently pendulums are not entirely reliable as the time for each half period gets smaller the more time elapses. Results came out as:

4.636 4.193

4.29 4.145

4.237 4.142

4.238 4.102

4.233

This averages out to an average full period of 8.5285. Plugging this into the equation along with the length of 15 the resulting value of g is 8.14152 to 5 decimal places. Alternatively doubling the arguably more accurate 4.636 gives a period of 9.272 which gives a g value of around 6.888. With this in mind I'd be inclined to take the former value as the (more) accurate, though further tests by other people would be appreciated (I've sorted permissions on the pendulum). Incidentally, although the bulk of the experiment was done by me, Flio, XxDaisylouxX, and Trixxiee were all witnesses so it's *kind of* a group experiment.