Output / Input Voltage Question

If I have a preamp that outputs 1.5v, but the amp's input is .5v, would this be the reason I don't have much headroom when I turn the volume up?  What is an ideal voltage match for preamp/amp combo?  Sorry if this is a dumb question.  Electrical stuff is not a strong point for me.
Beware audiophile tech talk, they will screw you up every time! Basically what happens, they will have you going round and round with a whole lot of stuff that is pretty much irrelevant. Not totally, and that is where they get you. Because every once in a while some of the stuff they talk about actually does matter. Problem is it takes you a good 10, 20 years of wasted time and effort to finally understand the vast majority of the time this stuff they go on and on about is well and truly irrelevant. Most of the time.

Like now. All that you have is an amp that does not require very much input voltage to drive it to full power. That is it. Period. Full stop. End of story. Nothing in audio matters less than where your volume knob is pointed. You get that now.

If you want you can take the time to study this stuff and when you understand it well enough then you will know ahead of time to expect the knob to be where it is. You will even be able to look at your source, be it CD or phono stage or whatever, and have a pretty good idea where the volume knob will be. It is actually pretty simple stuff once you get the hang of it.

Big picture though, keep it simple. Pay attention to speaker sensitivity. As long as that is 92dB or more you know you will always be able to find an amp to drive it nice and loud real easy without needing hundreds of watts. With turntables you want cartridge output of around .4mV or more in order to do the same, make it easy to find a phono stage. This is how to use specifications intelligently, to make your life easier not harder.
Do those two things and pretty much all the rest you can tell yourself, don’t sweat it. Eventually you may learn enough to understand why but in the meantime just tell yourself don’t sweat it.
What preamp do you have? 1.5V output from a preamp is very unusual. That's even lower than what most (if not all) digital source components provide which is around 2V for single ended outputs.
 As has been stated, if you have no issues with control over your volume, you are happy with your sonics, them you need not be concerned. 

Many amplifiers require over 1V to reach full output. Your amp requires only 0.5V, making it more sensitive to input voltage. Therefore you are attenuating much of the gain provided by the preamp, via the volume control. 
The OP is complaining about too much volume with a low setting on the volume control. That’s why I suggested an attenuator like the SYS!
But as usual the self proclaimed Guru of high end audio likes to show his wit with a ridiculous answer to the problem that the OP is having!