Number of Daubechies coefficients
According to MATLAB documentation on wavedec,


  The length of each filter is equal to $2N$. If n = length(s), the
  signals $F$ and $G$ are of length $n + 2N −1$ and the coefficients
  $cA_1$ and $cD_1$ are of length
  
  $$\text{floor}\left( \frac{n-1}{2} \right) + N$$


Here, $n=16$ is the length of your signal, and $N=2$ is the Daubechies number.

Putting all that together, your detail coefficients at the second level should be of length

$$\text{floor}\left( \frac{16-1}{2} \right) + 2 = 7+2 = 9.$$

At the second level, you coefficients should be of length

$$\text{floor}\left( \frac{9-1}{2} \right) + 2 = 4+2 = 6.$$

If you're wondering why this must be the case, imagine the filtering-decimation procedure. Scaling and wavelet function for $\text{db}m$ wavelets are of length $2m$. When you convolve length $n$ signal with length $2m$ signal, you get back a signal of length $l_0=n+2m-1$. If you take every second sample of this resulting signal, you get back something of length $l_1 = \frac{n+2m-1}{2} = \frac{l_0}{2}$. Of course, if $l_0$ is odd ($n$ is even), then we cannot split the signal exactly into two parts. With clever mathematics that I will not go into here, you can show that this last non-paired coefficient is redundant anyway (carries no information that we don't yet know), so you can just omit it. Therefore, we will always have the resulting decimated signal of length

$$l_1 = \text{floor}\left( \frac{l_0}{2} \right) = \text{floor}\left( \frac{n+2N-1}{2} \right) = \text{floor}\left( \frac{n-1}{2} \right)+N.$$