No,   D1.5 a bridge code and D1.6 is Stainless steel structures.

The D1.5 code is not intended to be used for the following: steels with a minimum specified yield strength greater than 690 MPa (100ksi), pressure vessels or pressure piping, base metals other than carbon or low alloy steels, or structures composed of structural tubing.

D1.6  Clause 4.7.3  "Previous Qualification Records" does however leave some discretion to *The Engineer*

Now if your D1.5 welders were somehow qualified with stainless fillers and D1.1 Group I or 2 base metal (engineers approval again) this might open the door a crack.  (but now we are tossing a 3rd code into the conversation to get what we want)

AWS D1.6-2007
Clause . 4.7.5 Base Metal

The base metal used shall comply with 1.2.  Qualification established with any one of these base metals shall be considered as qualification to weld any one of the base metals permitted by this code.  For all types of welded joints, the length of the weld and dimensions of the base metal shall provide sufficient material for the test specimens required by this code.  With the approval of the Engineer, performance qualification test coupons may be with any of the steels listed in AWS D1.1, Groups I or II.  Qualification established with any one of these base metals shall be considered a qualification to weld any of the base metals permitted by this code.

Unless your *Engineer* is very liberal with his seal, I don't see this being approved.

The simple and quick answer is 'NO'.

Lawrence gave you the complicated answer, but the engineer would really be grasping at straws to make a legitimate association that would justify the decision to accept that qualification.

He Is In Control, Have a Great Day,  Brent