Hi,
If the period of the sawtooth (triangle) wave takes the whole period then a simplification is:
Rms=sqrt(b^2+a*b+(a^2)/3)
where
'a' is the peak to peak amplitude of the triangular part alone, and
'b' is the level of the minimum part of the wave.
So for a wave that goes from -1.5v to +0.5v then a=2 and b=-1.5.
This formula works for waves that are basically triangular like a sawtooth but may also have a DC offset.
As another example, if the wave went from 1v to 1.5v then a=0.5 and b=1.
The question of how to calculate the average value however brings up a question of how the wave is going to be used in the application. For many purposes the average is just the average of the wave over time regardless of polarity, but for some purposes the average is the average of the absolute value of the wave over time. The main deciding factor is how the energy is going to be used in the application.