I prefer to use a more explicit notation that consists of the number of integer and fractional bits, like in your last question. I'll take them one at a time:
By Q8, I assume you mean unsigned Q0.8 (no integer bits, 8 fractional bits). In this format, there is no representation for the numbers $1.0$ or $1.5$. The largest value that an 8-bit unsigned integer can hold is $255$, which in this representation would correspond to a fixed-point value of $\frac{255}{256} = 0.9961$.
Similarly to the above, in signed Q0.7 format, there is no representation for $1.0$ or $1.5$. The largest 8-bit signed number is $127$, which would represent $\frac{127}{128} = 0.9922$.
You need to be explicit about whether your number is signed or unsigned. If you have a signed Q1.7 format, that would imply that your values are 9 bits long (1 sign bit, 1 integer bit, 7 fractional bits), which is unlikely. However, assuming that you had such a 9-bit signed number with 1 integer bit and 7 fractional bits, you can represent fixed-point numbers in the range $-2$ to $(2 - 2^{-7})$.
Recall that the conversion between the integer value and the corresponding fixed-point representation is merely a division by two raised to the number of fractional bits. A 9-bit signed integer can hold values in the range $-256$ to $255$, which leads to the fixed-point range I described above.
