Given the asymmetric power dynamic of instructor-student relationships, your routes for recourse are limited. As StrongBad mentioned, you are basically at the "mercy" of the instructor. Though, I would not go so far as to call this "grade grubbing" if you have a rational explanation for your decision making and/or if you think you can challenge the underlying assumptions for the attendance requirement. Here are my thoughts:

If the purpose of the attendance requirement is to make sure you learn material from the lectures and to test this, the course makes use of homework and exams; I would challenge the value of mandating attendance if you are able to complete the knowledge assessments with 91% ability.

If the attendance requirement is about in-class participation; I would challenge the value of removing 15% of the grade for two missed classes. It would be more equitable, in my opinion, to proportionally decrease the 15% based on the fraction of attendance vs total participation course days. For example, if there were 90 days of instruction, and you missed 2, your grade value for "attendance" would be 88/90 * 15%. I quote "attendance" because at this point, it would be more appropriate to call this participation.

To the "well, you knew this going into the course" point some people are making, I would balance this against a few factors:

1. Were there other offerings for the same course by different instructors?
2. If so, did those instructors offer a different "attendance" policy?
3. If not, could you have taken this course another semester from a different instructor with a different policy?

If not, I do not believe it is fair to blame you (or a student in general) for ending up in this situation. As mentioned above, the instructor-student power relationship is not symmetric. For an example in another area of life: the landlord-tenant relationship shares a similar power dynamic. Given a person looking for housing is usually in such a disadvantaged position when compared to the person who has excess housing to rent, traditionally landlords are able to request unreasonable requirements of those renting. We have created laws to put limits on these requirements to protect those in such a disadvantaged position. The instructor-student relationship is not much different: especially if the above three alternative options do not exist.

In my time in education systems (K-12, Undergraduate, and Graduate), where I have both learned and taught, I have seen many cases of completely unreasonable grading policies adopted by instructors. Many based on good intentions who's net effect was unreasonably burdensome: sometimes to all students, sometimes only to a few. In my opinion, it behoves us as educators to focus on the root value of our grading policies: do they measure what we are intending, are they balanced, do they take into consideration how many people come to class with different world-views? This isn't to say we should have no rules (or complete open rules), but from what I have seen, attendance requirements are rarely needed and are frequently unfair to students who are otherwise capable of learning the material but who have different day-to-day life demands.

From this perspective, I can completely see where you are coming from. However, outside of trying to use reason with your instructor, a route I have seen fail for many, I'm afraid you may be out of luck. Though, as a last resort, you could always approach the department chair or dean if you feel they may be sympathetic to your situation.

Given the asymmetric power dynamic of instructor-student relationships, your routes for recourse are limited. As StrongBad mentioned, you are basically at the "mercy" of the instructor. Though, I would not go so far as to call this "grade grubbing" if you have a rational explanation for your decision making and/or if you think you can challenge the underlying assumptions for the attendance requirement. Here are my thoughts:

If the purpose of the attendance requirement is to make sure you learn material from the lectures and to test this, the course makes use of homework and exams; I would challenge the value of mandating attendance if you are able to complete the knowledge assessments with 91% ability.

If the attendance requirement is about in-class participation; I would challenge the value of removing 15% of the grade for two missed classes. It would be more equitable, in my opinion, to proportionally decrease the 15% based on the fraction of attendance vs total participation course days. For example, if there were 90 days of instruction, and you missed 2, your grade value for "attendance" would be 88/90 * 15%. I quote "attendance" because at this point, it would be more appropriate to call this participation.

To the "well, you knew this going into the course" point some people are making, I would balance this against a few factors:

1. Were there other offerings for the same course by different instructors?
2. If so, did those instructors offer a different "attendance" policy?
3. If not, could you have taken this course another semester from a different instructor with a different policy?

If not, I do not believe it is fair to blame you (or a student in general) for ending up in this situation. As mentioned above, the instructor-student power relationship is not symmetric. For an example in another area of life: the landlord-tenant relationship shares a similar power dynamic. Given a person looking for housing is usually in such a disadvantaged position when compared to the person who has excess housing to rent, traditionally landlords are able to request unreasonable requirements of those renting. We have created laws to put limits on these requirements to protect those in such a disadvantaged position. The instructor-student relationship is not much different: especially if the above three alternative options do not exist.

In my time in education systems (K-12, Undergraduate, and Graduate), where I have both learned and taught, I have seen many cases of completely unreasonable grading policies adopted by instructors. Many based on good intentions who's net effects were unreasonably burdensome: sometimes to all students, sometimes only to a few. In my opinion, it behoves us as educators to focus on the root value of our grading policies: do they measure what we are intending, are they balanced, do they take into consideration how many people come to class with different world-views? This isn't to say we should have no rules (or complete open rules), but from what I have seen, attendance requirements are rarely needed and are frequently unfair to students who are otherwise capable of learning the material but who have different day-to-day life demands.

From this perspective, I can completely see where you are coming from. However, outside of trying to use reason with your instructor, a route I have seen fail for many, I'm afraid you may be out of luck. Though, as a last resort, you could always approach the department chair or dean if you feel they may be sympathetic to your situation.