I ran it like PSK31, with my rig's power turned all the way up.
I control the power out by adjusting the audio level going in to the
Mic plug, and/or use the Mic Gain control to adjust as high as I can
with zero ALC activity.
I usually ran about 50-60 watts, that way.
Note that Q15x25 is not just an HF mode. I have found it to be better
than Packet for mixed-mode digital operation over a VHF FM repeater,
of all things. - It works very well at this!
The only parameter you need to change is TXDELAY, which I had to set
for 800ms. One repeater I tried required a full second ( 1000ms ) of
delay in order to work.
This gives you digital capability when needed on your voice repeater,
at twice the speed of regular packet.
The TXDELAY being so long does slow things down, but Q15x25 tends to
large MAXFRAME and PACLEN values, so it all comes out in the wash as
a very effective mixed-mode system for VHF/UHF.
Charles Brabham, N5PVL