ATPLs - Flight Performance & Planning Question

[Dipole]

Magnetic track 215deg
Mountain elevation: 11600ft
Local Airfield QNH: 1035mb
Required terrain clearance: 1500ft
Temperature ISA: -15c

What is the minimum flight level considering temperature?

Answer is FL140

My method:
11600 + 1500 = 13100ft -->Mt. elevation + required clearance
13100 - (20*30) = 12500ft -->Difference in altimeter pressure readings
Next even flight level= 140

Correct???

It's correct to say that altimeter measures for ISA isn't it? So, no need to correct for temperature???

Thanks!