snalberski said..
I think you should be fine with that kite. It is on the smaller end and will require a bit more work to generate the same power as a 10m in any given wind strength. Once the wind goes up to slightly higher wind strengths
(23-27knts) you will probably find that you have to work much less and the 8m will be perfect. Although manufacturers will claim kites with wind ranges of upto 15knts variation for me it seems that in reality the sweet spot of a given kite is much narrower (2-3 knts either way). Also bear in mind that as you get better at flying you will be able to juice more power from any given kite.
I guess that's what I was getting at, as a beginner you'll struggle a bit more in the lower and upper ends of the wind range, for the Nitro 8 in the conditions you are talking about you are right on the bottom end of it's recommended wind range. So there are two solutions either tough it out with what you have which will be slow and frustrating or get another kite (which you've identified) which you'll want later anyway. You are best imo to stay with the same model you have as there are variations in the way kites handle even between models and when you are learning swapping between kites that handle differently doesn't really help......I'd try and find a Nitro 10 in the same model as you have (either V1, V2 or V3)