The main concern is not about rolling a 22+ - that's a longshot*. The worry is rolling a 13. And here we get into metagaming and numbers, unfortunately.
(* Re 22+: any normal number on the dice that's doubled once is 20 or less. So you need to get to x4, or roll "1" twice - that's 1% just to start - before you then roll some number large enough to bump well over 22. With any decent total, that's going to drop well below .5% (1/2%), maybe toward or below .1% (1/10%, .001)
+12 is actually a good number, and better than +13 (or even +15!!!). You can't roll 13 with +12 to the roll* - roll a "1", the next number is doubled - you might roll a 22+ (with double 1's), but never a 13.
* If your total is any even amount (-12, -14, etc), you have no chance to roll a 13. Roll a "1", double the next roll, that number will be even - and an even number minus an even number cannot equal an odd number. (13 is odd, for those who turn green at the sight of "math").
But every 10 years, if nothing else changes, the total will drop by -1, and so shift from odd to even. What then is a "safe" buffer to avoid the dread 13?
Some are comfortable with -14, on the theory that ~if~ you roll a "1", then you still have to roll just one specific number (or another 1) - that's at most a 1/10 x 2/10 = 2% chance - many can live with that.
On the other hand, if you have the lab total and the vis, and just want to crush it, then every bit larger is better. You could even invent two huge LR's, one even and one odd, and alternate for a while, every ten years - no one says you have to use the "best" one, it's just assumed. And since 13 is out of the picture, unless you roll 1, 1, and then some appropriately large number (less than a 1% chance), you're safe.