[PK]

Unlike skills, techniques never have a /TL designation. This is because they exist (for the most part) to buy off a penalty involved in using a given skill, regardless of that skill's TL. (Obviously, some techniques only make sense for a limited range of TLs, but that's a red herring so I'm only acknowledging it to avoid someone pointing it out.)

And unlike skills with different specialties (where each specialty is considered a separate skill), a skill bought at multiple TLs is still the same skill. So any applicable technique would produce the same relative results.

Note that the same goes for perks that require specialization by skill; e.g., Grip Mastery (Pistol) works for any version of Guns/TL (Pistol) that you have, regardless of that skill's TL, because the /TL is not part of the perk's specialization.

TL;DR: 15.