I have spent a few good sessions on the Spectrum 15m and have found the following. I currently have Rhino 2's, ride 130x38 board and intermediate kiter and weigh in at 90kg.

First and foremost - this kite is powerful. If you don't like a grunty kite you might find the 15m a bit of a weapon.
Me - I like power, big air and hang time and this kite certainly fits this criteria. I have flown R4 14, Best Nem 14, R4 16, R2 14, R2 16, Co2 04 14 and a couple of older kites around this size.
I haven't found a kite I like enough to change my R2 quiver but this maybe the one. The boost and hangtime is the best I have ever had
on this ~size kite. With the new great deals here in oz on liquid force gear
I don't think you could look past it.
Price wise the Best Nemesis is in the same category but IMO the finish and sail cut in the air and on the ground of the Spectrum is better.
Another devout North rider who is quite heavy had a go and compared it to the Rhino 2's but with more hang. I hope he adds his comments as I would be interested in his opinions.
I used my own bar on the kite as the original one wasn't set up yet and I feel you need to have your own bar and board to do a fair kite review.
Looking forward to try the other sizes - hopefull the 10m today as the forecast is 20-30kts.

How did it compare to the Nemi construction wise and performace wise.It would be intersting to see a head to head on these 2 Market price leaders in Oz.I believe that they retail for about $1450 15m LF/14m Best.

Construction wise - I would have to say that the Liquid Force was better.
Similar reinforcements but a bit of extra detail and panel layout.
I noticed with the Best 14 that there was a bit of ripple in the canopy on launch and when luffing in the sky a bit in gusty winds. I noticed this yesterday on a Best 12 aswell. Don't think this would effect performance though. Just gives me an overall impression of all round quality. The Spectrum's canopy was rock solid like the good kites of North.

Not that it means much, but the colour scheme on the liquid force is sweet, especially with the sun behind it. The best Nem is all one colour.

Get a go on the 15 if you can - I couldn't believe the hang time esp being a devout R2 rider.

Found the top end of the 15m today for me (conway) at about 20+kt gusts with the average wind 16-17kts. The kite is very grunty and I'm hanging out to try the 19m - hopefully this week.
Kurt