I have more or less the same problem, but at sub-20 mark (I wish it was at sub-15). Best case scenario, when my solves go super-fluid and perfect lookahead I can get a high-13 or mid-14 full-step solve but most of the time I cannot get better than 16-17 and my long averages are around 19-21 seconds.
I have found that recording my solves helps a lot to identify my problems but not to get rid of them. It is very enlightening to see how much I paused between F2L pairs (and between cross and 1st F2L pair most obviously) when I thought it had been a fine solve.
But, even if I had close to perfect lookahead I would be doing 13-15 sec solves, which would be great but... how about sub-12 or sub-10? I just have to assume that I'm too slow and inaccurate to reach sub-10 territory. Perhaps I lack the coordination or I'm just too old (45) to get there. I don't have a 13-14 sec solve on cam to be sure, maybe I'm victim of a delusion that I did not pause on those solves but I did, just not as much as in other 17-20 solves I have on cam.
Let's see, a normal, not super-efficient CFOP solve of 65 moves, in 15 seconds is equial to 4.3 TPS. Fast guys are not much more efficient, they don't get sub-10 sec solves because they solve in 50 or less moves, they do it because they execute at 6-7 TPS or higher. Just as an example, my best times for 6-times-sexy-move is around 2 seconds (12 TPS) when many people go easily faster than 1.5 or 1.2. Another example, my fastest timed T-perm is around 1.6 seconds when most fast cubers can sub-1 it.
With all this in mind my conclusion is that, until around sub-15 lookahead is critical (and good planning of cross and maybe even 1st pair, which I'm also pretty bad at). From there on, and clearly around sub-12 to sub-10 or faster, TPS is very, very important. Of course, both are related, as long pauses decrease your TPS but when you are twice as slow as the next guy in your LL that's almost purely a TPS problem (unless recognition is also an issue).
I hope this helps somebody know what to work on. I for one have already assumed that it will be close to impossible for me to reach sub-15 territory but it's fun to keep trying. If you don't agree and think I could reach close to sub-10 at least I'll be glad to post a video of an Ao5 in the solve critique thread and see what else I'm doing wrong apart from sloppy turning and slow TPS that can be fixed even when you are old and slow
