Someone that has difficulty eating a kezayit matzah (or any food for that matter and has to eat always very slowly) in the time of kedei achilas peras (even according to the most lenient opinion). Do they still fulfill the mitzvah of eating matzah even if it might take 15 or more minutes to eat the matzah?
This appears to depend on a dispute among rishonim.
See in particular the Rambam (Matzah 6:1), whose wording implies that there is no time limit, providing that one eats the matzah without interruption.
However, the Magen Avraham (475:4), citing from Maharil, rules that one must complete the kezayit within kedei achilas peras, and this is also cited from the Ramban by Halachos Ketanos of the Rosh (Menachos). See also Rashi, Sukkah 42.
Therefore, in a practical sense one must certainly ensure that the matzah is eaten within kedei achilas peras (9 minutes at the very most), for this is clearly the majority opinion.
If this is hard, the matzah can be soaked in water to soften it.