As you move to more senior roles, those for people with over 10 years of experience, it's common for the roles to require significant soft skills, such as leading others, managing a relationship between two firms (vendor and customer, for example), co-ordinating tasks and priorities without anyone feeling slighted, and so on. It's possible that you either do not have these skills, or are not succeeding in communicating during the interview that you have them. If so, this isn't discrimination, but it is still a problem you need to address.
Another career route for many developers as they approach 15 years of work is into architecture and big picture design. It's possible that you don't want to do that kind of work, or are not communicating during the interview that you want and can do that kind of work. This, as before, is not discrimination but is a problem.
Let me elaborate. Many people with Asperger's are not good at "soft skills" and don't pick them up naturally. They may even assert that such skills are not needed to be a developer and are irrelevant to being a good software engineer. Many hiring managers may disagree, especially for more senior jobs, and even when the job description doesn't mention any need to lead, manage, soothe, co-ordinate, or inspire. If this is the case for you, not getting the job may be because you are missing a required skill. You can choose either to gain the skill, or not to apply for such jobs. Another possibility is that you have the skill (it can be learned, but it's hard work, much like learning to walk after an injury) but you don't demonstrate it in the interviews. Some interviewers might see a lack of eye contact or weak chit-chat skills as "markers" for a lack of the ability to lead, manage, soothe, co-ordinate and inspire. If you in fact have these skills, you can work on how to show that in a job interview. This may involve telling people your diagnosis or it may not.
Is it discrimination? If you say on your resume that you have this diagnosis, and a hiring manager says "those people have no soft skills" and doesn't even interview you, then yes, that's discrimination. If at the interview you are asked about leading, inspiring etc and can feel the mood cooling as you try to answer, then it is more likely that you are legitimately missing a skill or the ability to demonstrate that skill in the interview. Focusing on this rather than "they hate me for who I am" will improve your own satisfaction and could lead to a change in strategy that will improve your job search results as well.
What should you do? First, decide very clearly what kind of job you want. Do you want to only code? Would you like to add big picture design and architecture to coding? Do you want to lead others? And so on. Understand what you want and don't want specifically as a person with this bundle of skills and capabilities. If you don't want to take on the work of learning something that appears to come naturally to everyone else, you don't have to.
Second, decide where to apply. Small firms typically ask their developers to wear more hats. Large firms may even have a "technical track" where you can just get better and better at what you do without ever having to develop soft skills. I would suggest that you prioritize applying to large companies - they will be able to assign far narrower duties, and they are likely to have HR departments that can enlighten your manager about the advantages of hiring someone on the spectrum. They can also help you if you feel discrimination happening after you are hired. (That said, my firm is very small and has hired people on the spectrum. I am probably not representative of small firms, but you may find a small place that's a great fit. It's more likely to happen from the relationship leading to a job than from applying to something you see advertised and competing with other candidates.)
Third, consider learning some particular skills, such as how to run a meeting, or how to persuade someone to do things your way, if you feel that having those skills will help you to land a job you want.
Fourth, learn how to show in an interview that you can do what the job requires even if you look or sound a little different from most people who can do that. Believe it or not, simply stating that you can goes a long way towards that convincing process. You should also have anecdotes for the usual questions about problem solving, conflict resolution and so on, and be able to talk about your success with a particular skill. This is less important if you want to only code, but may still be relevant even in that case.
The interview process is extra hard for people who don't like talking. You can do your best to shorten it by building up a reputation some other way, such as blogging or tweeting, contributing to open source, and so on. You can also get better at it by practicing. Combine that with applying to the right sort of jobs and you should find a much higher acceptance rate. I know several people whose Asperger's is far from mild who have landed some great jobs with household name companies. It can be done.
