Josh0419,
I think ILya makes a good case for getting a mount with 20 moa built in for the 3-15M (provided your rail is 0 moa/flat of course). As he says "Why not", especially in the case of the 3-15M so you can have full travel? I am so used to 20 or 30moa built into a rail that I had almost forgotten about canted mounts. ILya reminded me in another thread where he has his 3-15M mounted to a .308 Fix (0 moa in the rail).
Excellent choice by the way on the 3-15M. It is my favorite all around optic, and really tough to beat unless you have specific reticle/max-power/high number of mils on the turret needs. What reticle did you go with (Gen. 2 Mil-dot here)?
Some good 30mm/20moa unimount options that are not QD and not max price: Aadmount, Nightforce, Geissele. Up a bit in price: Spuhr. Of note, the two bolt setup on the NF and Geissele is pretty fast to get on and off if you have the wrench handy (probably could stash one in your grip?). They are all reasonably fast to get on and off with the correct wrench handy though (talking about in a pinch, not torquing exactly...although Fix It Sticks with the right parts are very compact), and that is one of several reasons that for me QD is not really a draw.
Some good 30mm/20moa unimount options that are QD and not max price: Bobro, other? If you go up in price, then you can talk Spuhr, GDi, and Era-tac. I have no experience with Era-tac personally though, so I defer to others and their good reviews. Also Era-Tac does not seem to have a cantilevered QD mount (though they do have a bolt-attach one). As noted, horizontally split rings are the way to go here, as well as cantilevered to some degree for mounting flexibility.
Further Notes:
I love ARC rings and mounts and use them when I can. The single bolt design is so nice for mounting and I have never had a set be anything other than excellent. However, with the 3-15M I prefer "standard" horizontally split rings with a thinner top half so I can see the elevation turret and markings more easily. The ARC rings are a bit tall for that. They work great on the TT "P" series as the turret housing and markings are higher up, but on the 3-15M they are tall enough to be annoying (for me).
If you like to have a scope mounted level, the options with the 4 screw rings will give you a little more flexibility there than the 6 screw rings (typically talking about mounting the level on the front/obj. side of the turret where there is limited space). If you mount your level on the eyepiece/rear side of the turret, then no worries.
Hope that helps dude, surely those aren't the only options but those are all great mounts. Congrats on the sweet rifle and great scope choice! Hope you get it mounted up quick and go out shooting!
-TSean