Not to be harsh but let me get this straight - You're obviously using a mech mod as I don't know of any regulated mods that will fire a coil that low. Someone please correct me if I am wrong. Therefore, you're using batteries and attempting to build within their safe limits. You then ask if using a .15Ω coil on a 40A battery is safe?
Let me help you out a little here. The amperage required is equal to the voltage divided by the resistance. For instance, if we take a fully charged 40 amp battery at 4.2 volts and divide it by a coil's resistance of .15 ohms, we get a result of 28 amps. So therefore, the 28 amps is within that battery's safe zone but it is starting to push it. However, that's all dependent upon that battery manufacturer's claims being valid.
For a more concise explanation, I suggest you get acquainted with our resident battery expert Baditude's Blog. This one in particular:
(14) Ohm's Law for Dummies
Good luck and vape safe!