Ok, I'm going to answer as both a sound guy and a guitarist (I have a POD X3 Live, but same concepts apply).
-Your 15 watt amp at home will most assuredly sound different than any PA system that you plug directly into (btw, congrats on apparently owning a 10,000 watt sound system? lol).
-If you like the sound with the 15 watt amp, there's nothing wrong with bringing it to the gig and have them mic it, otherwise, practice with headphones and the amp modeling turned on to get a better idea of how it's going to sound. (Fun fact, many walls of amps seen on live tours back in the day were dummy cabinets and there was a 5 to 15 watt tube amp behind them with a mic in front of it, and it sounded beautiful).
-If you're plugging directly into the sound system via XLR, MAKE SURE THEY HAVE PHANTOM POWER TURNED OFF. I can't say yes or no if it will damage your pedalboard, but best to assume it would. You could also contact Line6 and ask them if the XLR outputs will block the 48Volt DC phantom power.
-If they can't turn off phantom power, consider using a direct box, which will convert your 1/4" output to XLR mic level that you can plug into the sound system safely.
-If your patches are stereo, and the board is run in mono, and you're plugged into the mixer in stereo (both XLR or both 1/4" outputs), and both channels are panned center, you may experience cancellation in some patches (I've experienced this personally with some effects boards run in stereo). Consider purchasing a small mixer and PA that you can experiment with at home.
-Honestly, if you're running live, just run Mono. Stereo doesn't buy you anything unless your sound system is an LCR system (left/center/right) and each seat in the house is covered by a stereo cluster (one left and right main speaker in a venue doesn't count).
-If you're using a stereo to mono combiner or direct box to feed the sound system, don't. You can get weird cancellations that way as well. Just use the mono output from the pedalboard itself and it will internally convert to mono output properly without any weirdness. Trust me, no one will know whether you're running stereo or mono, and most live concerts you see are in fact run in mono.(edit: if you have to use a stereo to mono combiner, make sure it's a proper resistive-combining type, not just a Y-splitter cable turned around backwards to combine 2 into 1...that can actually damage stereo outputs. Look up Rane Note 109: "Why Not Wye?" note in Rane's highly respected Knowledge Library for more on how to do this properly).
Hope this helps,