Quran 49:15 – Doubts After Belief
If doubts are there, it means one has yet not consciously believed. You need to learn the arguments and pieces of evidence of Islam being the truth. Once you realized its truth, doubts cease.
Quran 49:15 is in a different context, where nearby Bedouins who professed faith in Prophet Muhammad (sws) because of Islam’s political domination, used to mention it as a favour to which Quran clarified that this is not the kind of faith which makes one ‘ Momin ‘ where one is willing to sacrifice their weath and their lives without an iota of doubt, rather it is a mere submission which has room for improvement and any good deeds done under this obedience to Allah and his Prophet, will be rewarded by Allah ( so in it there is no favour done for the Prophet (sws) rather the favour is for their own souls ). Please read the verses 49:14-15 together: https://www.javedahmedghamidi.org/#!/quran?chapter=49&paragraph=9&type=Ghamidi