The test questions are categorized. Every open book test has a certain percentage of questions pertaining to welder qualification, procedure qualification, test methods, etc. The number of questions pertaining to each category represents a percentage of the total number of questions on the examination. How heavily weighted each category is  can be determined by reviewing AWS B5.1. That document will tell you there must be X% of questions pertaining to welder qualification, Y% on the subject of procedure qualification, Z% on the subject inspections, etc.

To say it another way, all AWS codes are organized in a similar fashion; Clause 1 - General, Clause 2 design, etc. That being the case, regardless of which open code one takes, the percentage of questions taken from Clause 1 will be C%, Clause 2 will be D%, Clause 3 will be E% as defined by AWS B5.1.

The bottom line; the examinations are defined by AWS B5.1.

Unlike AWS D1.1 which is covered in an 8 hour session during the CWI seminar, I do not believe AWS has any formal training offered for D15.1. However, attending the D.1 review provides some insight on the arrangement of the AWS codes and how to navigate the AWS codes. Navigation is key to passing the open book code examinations.

Best regards - Al

To slightly expound upon Al's answer and your question,

Yes, the testing is basically the same.

Part A: the General Knowledge Closed book exam taken for the most part from WIT workbook set will be the same.
Part B: the Practical hands on portion taken from the bogus book (Part B book of specs) will be the same.
Part C: The Open Code Book portion will vary but only in areas of specific information for D15.1 and as Al already explained, the question types will be the same but they are specific for D15.1.

Oh, and you can take the same seminar even though it won't get into D15.1 and you will take the test on the same test day as others taking exams to which ever code they have chosen.

He Is In Control, Have a Great Day,  Brent