Hey guys, I just bought a 2000 TH Magna Solara, and according to my trip computer my fuel economy is sitting at around 15.3L/100km. This seems really high to me, is this normal or is something wrong with the car?
Thanks in advance.

Depends on where and how it is being driven. In city traffic it could easily get that high or higher. Cruising on a highway it should be well under 10L/100km.

It's mostly just suburban driving, occasionally I'll drive from Melbourne to Geelong or Bendigo, but I've never seen it below 12L/100km.

Try resetting the trip computer when you fill up. Then next time you fill up see if the reported fuel used matches the fuel it took to fill the tank back up. Should be within a few litres.

What is the trip computers average speed?

Average speed: 28.5km/h
Average fuel: 15.8L/100KM
Total fuel: 77.8L (even though my fuel gauge says it has just above half a tank?)

Total fuel indicates fuel used since the last time the trip computer was reset rather than the fuel left in your tank AFAIK. 28.5 km/h average is pretty low, must be lots of traffic lights in your area! I mostly use my TJ wagon for suburban use with a few highway/freeway jaunts and get around 11.5 L/100km with an average speed of around 60 I think (been a while since I checked). Your low average suggests lots of idling at lights or crawling in traffic jams in which case 15.3 L/100km is probably fairly reasonable. As Jimbo says, reset the trip computer and check if your actual fuel use matches the computer's estimate, and also flip to the instantaneous economy mode and find a flat, level road where you can do a fairly consistent 80km/h. The inst reading should be around 8 to 9 from memory (anybody please correct me if this figure is wrong).