Depends on what style of riding you are going to progress with but hard to beat the Ozone Edge - 15m would work

I'm 93 kg and in 15knots will always pull out my 2012 13.5m Griffen Argo - so agree with the guys above - but i'm on a surfboard so the TT would need to be around 140 cm ++ long and 44cm ( 17") wide ++ to make upwind possible and the session fun.
Any 14m kite from around 2010 or later should be good - my experience suggests that bigger kites ( like the 16's or bigger) just need more wind to support them to fly so really dont give you an extra edge for light wind (with the exception of some amazing (but expensive) new kites out there with maybe only 1 or no strut!)

well i cant make out what size that slingshot rev2 is but im 85kg have 12m f-one B4 and ride a 139x41.5 north xride and I can only just get going in 15knts.
So best guess is 14m for you, but dont go the Ozone edge its more a race kite and as a noob you want something thats super easy to fly to help you progress your all round skills quicker.

I am bout 105kg and could cruise round on my 11m switchy on a 135 lunacy in 15 knots.